Add remote-peer support over Tailscale and unicast probing

Multicast only finds peers on the same LAN. Reach off-LAN boxes by probing
them directly over unicast (works over any routable address; Tailscale is the
easy, secure choice):

- discovery.Probe: unicast POST /register (https->http fallback) with a two-way
  handshake, so send and receive both work; offline peers age out.
- internal/tailscale: Peers() shells `tailscale status --json` for online peers.
- config.KnownPeers: persisted manual remotes.
- main.go: watchRemotes goroutine probes knownPeers ∪ tailscale peers every 10s,
  in both the normal TUI path and quick-send.
- TUI: `+` on Devices opens an add-remote modal (host/IP/Tailscale name).
- install.sh: interactive local/remote install prompt; remote mode locks port
  53317 to the Tailscale interface (ufw), with container/userspace-networking
  detection. README documents remote devices.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -10,6 +10,10 @@ LocalSend mobile and desktop apps on the same LAN, including their default
 
 - **Discovery** — multicast announce/listen on `224.0.0.167:53317` plus the HTTP
   `/register` handshake, with peer aging.
+- **Remote devices** — reach boxes that aren't on your LAN (multicast can't find
+  them) by probing them directly over unicast. If [Tailscale](https://tailscale.com)
+  is running, online tailnet peers are discovered automatically; you can also add
+  a device by host/IP/name with the `+` key, saved for next time.
 - **Receive** — incoming files are accepted via a prompt (or auto-accepted) and
   written to the receive directory, with live progress.
 - **Send** — pick a peer, then find what to send with a built-in **recursive
@@ -47,9 +51,16 @@ curl -fsSL https://raw.githubusercontent.com/28allday/omarchy-send/main/install.
 ```
 
 This downloads the right binary for your architecture into `~/.local/bin`, and on
-Omarchy also adds a floating Walker entry (search **Omarchy-Send**). Override the
-location with `BIN_DIR=/usr/local/bin`, or pin a version with
-`OMARCHY_SEND_VERSION=v0.1.0`.
+Omarchy also adds a floating Walker entry (search **Omarchy-Send**) and the
+Nautilus right-click integration. Override the location with `BIN_DIR=/usr/local/bin`,
+or pin a version with `OMARCHY_SEND_VERSION=v0.1.0`.
+
+**Local or remote?** When run interactively the installer asks whether this is a
+**local** machine (home/LAN) or a **remote server** (public IP). Local installs as
+above. For a remote server it additionally locks port `53317` to the Tailscale
+interface in the firewall (`ufw`), so the box is reachable over your tailnet only —
+not the open internet. Non-interactive installs (e.g. piped `curl | bash`) default
+to local; force a choice with `OMARCHY_SEND_MODE=local` or `OMARCHY_SEND_MODE=remote`.
 
 > The installer is a short shell script fetched over HTTPS; read it first if you
 > prefer — it lives at [`install.sh`](install.sh) in this repo.
@@ -111,6 +122,27 @@ Staging a folder sends it whole (its structure is recreated on the receiver).
 Matching is case-insensitive, and noisy directories (`.git`, `node_modules`,
 caches, dotfiles…) are skipped to keep the index fast.
 
+### Remote devices (over Tailscale)
+
+Multicast discovery only finds peers on the same LAN. To send to / receive from a
+box elsewhere, omarchy-send probes it directly over unicast — which works over
+anything routable, [Tailscale](https://tailscale.com) being the easy, secure choice
+(stable addresses, end-to-end encryption, no port-forwarding):
+
+1. `tailscale up` on both devices (one-time).
+2. Either let omarchy-send **auto-discover** online tailnet peers (it probes them
+   every few seconds; any running omarchy-send/LocalSend appears in Devices), or
+   press **`+`** on the Devices tab and enter a host, IP, or Tailscale name (e.g.
+   `colossus`). Added devices are saved to `knownPeers` in the config and re-probed
+   on every launch.
+
+The receiver already listens on all interfaces, so it's reachable at its Tailscale
+IP with nothing else to configure. Sending and receiving both work, because the
+probe is a two-way handshake (each side learns the other).
+
+> On a box with a public IP, don't leave `53317` open to the internet — install in
+> **remote** mode (above) to firewall it to the tailnet, and/or set a `--pin`.
+
 ### Right-click send (Nautilus)
 
 On an Omarchy desktop, the installer adds a **"Send via Omarchy-Send"** entry to
@@ -154,7 +186,7 @@ omarchy-send --auto-accept --pin 2468
 ### Keys
 
 - `1`–`5` or `tab` — switch between Devices / Transfers / Manage / Messages / Settings
-- Peers: `enter` send to the selected peer · `m` message · `v` send clipboard · `r` refresh · `/` filter
+- Peers: `enter` send to the selected peer · `m` message · `v` send clipboard · `+` add a remote device · `r` refresh · `/` filter
 - PIN-protected peers: messages prompt for the PIN and retry, just like file sends
 - Send finder: type to fuzzy-filter · `enter` stage file/folder · `ctrl+d` folders-only · `ctrl+s` send · `ctrl+u` up a dir · `esc` back
 - Incoming prompt: `y` accept · `n` reject

cmd/omarchy-send/main.go

@@ -12,6 +12,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"sync"
 	"sync/atomic"
 	"time"
 
@@ -24,6 +25,7 @@ import (
 	"omarchy-send/internal/discovery"
 	"omarchy-send/internal/notify"
 	"omarchy-send/internal/server"
+	"omarchy-send/internal/tailscale"
 	"omarchy-send/internal/transfer"
 	"omarchy-send/internal/tui"
 )
@@ -34,6 +36,85 @@ type controller struct {
 	sender *client.Sender
 	srv    *server.Server
 	notify *atomic.Bool // live gate for desktop notifications (toggled from Settings)
+	rem    *remotes     // live set of directly-probed (known/remote) hosts
+}
+
+// remotes is the live set of hosts probed directly over unicast: known peers
+// loaded from config plus any added at runtime in the TUI. Guarded because the
+// watcher goroutine and the controller's AddKnownPeer both touch it.
+type remotes struct {
+	mu    sync.Mutex
+	hosts []string
+}
+
+func (r *remotes) list() []string {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	return append([]string(nil), r.hosts...)
+}
+
+// add appends host if not already present, returning true if it was new.
+func (r *remotes) add(host string) bool {
+	host = strings.TrimSpace(host)
+	if host == "" {
+		return false
+	}
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	for _, h := range r.hosts {
+		if h == host {
+			return false
+		}
+	}
+	r.hosts = append(r.hosts, host)
+	return true
+}
+
+// AddKnownPeer registers a remote host and probes it immediately so it shows up
+// without waiting for the next watcher tick. Persisting it to config is the
+// TUI's job; this only updates the live set.
+func (c controller) AddKnownPeer(host string) {
+	if c.rem != nil {
+		c.rem.add(host)
+	}
+	go func() {
+		ctx, cancel := context.WithTimeout(context.Background(), 4*time.Second)
+		defer cancel()
+		_ = c.disc.Probe(ctx, host)
+	}()
+}
+
+// watchRemotes periodically probes the known-peer set plus any online Tailscale
+// peers, so devices that multicast can't reach (different subnet / over the
+// tailnet) still appear in the list — and age out when they stop answering.
+func watchRemotes(ctx context.Context, disc *discovery.Discoverer, rem *remotes) {
+	probeAll := func() {
+		seen := map[string]bool{}
+		hosts := rem.list()
+		hosts = append(hosts, tailscale.Peers(ctx)...)
+		for _, h := range hosts {
+			if h == "" || seen[h] {
+				continue
+			}
+			seen[h] = true
+			go func(host string) {
+				pctx, cancel := context.WithTimeout(ctx, 4*time.Second)
+				defer cancel()
+				_ = disc.Probe(pctx, host)
+			}(h)
+		}
+	}
+	probeAll() // immediate, so remotes appear without waiting a tick
+	t := time.NewTicker(10 * time.Second)
+	defer t.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-t.C:
+			probeAll()
+		}
+	}
 }
 
 func (c controller) Announce()                                         { c.disc.Announce() }
@@ -186,7 +267,9 @@ func main() {
 	// only carries the user preference here.
 	notifyOn := &atomic.Bool{}
 	notifyOn.Store(!cfg.NoNotify)
-	ctrl := controller{disc: disc, sender: sender, srv: srv, notify: notifyOn}
+	rem := &remotes{hosts: cfg.KnownPeers}
+	ctrl := controller{disc: disc, sender: sender, srv: srv, notify: notifyOn, rem: rem}
+	go watchRemotes(ctx, disc, rem)
 
 	p := tea.NewProgram(tui.New(cfg, ctrl), tea.WithAltScreen())
 	app.BridgeDiscovery(ctx, disc.Events(), p.Send)
@@ -222,7 +305,9 @@ func runQuickSend(cfg config.Config, paths []string) int {
 
 	// No receiver in quick-send mode, so nothing to notify about.
 	notifyOff := &atomic.Bool{}
-	ctrl := controller{disc: disc, sender: sender, srv: nil, notify: notifyOff}
+	rem := &remotes{hosts: cfg.KnownPeers}
+	ctrl := controller{disc: disc, sender: sender, srv: nil, notify: notifyOff, rem: rem}
+	go watchRemotes(ctx, disc, rem) // so a remote box is a valid quick-send target too
 
 	p := tea.NewProgram(tui.New(cfg, ctrl, tui.WithStagedFiles(paths)), tea.WithAltScreen())
 	app.BridgeDiscovery(ctx, disc.Events(), p.Send)

install.sh

@@ -14,11 +14,15 @@
 # Environment overrides:
 #   BIN_DIR=/usr/local/bin           install location (default ~/.local/bin)
 #   OMARCHY_SEND_VERSION=v0.1.0       pin a release (default: latest)
+#   OMARCHY_SEND_MODE=local|remote    skip the local/remote prompt (default: ask,
+#                                     or local when non-interactive)
 #
 # Behaviour:
-#   - Headless system: installs the plain `omarchy-send` TUI binary.
-#   - Omarchy desktop:  additionally adds a Walker entry that launches it as a
-#     floating TUI (via the stock TUI.float app-id), like the Wi-Fi TUI.
+#   - Local machine (home/LAN): installs the TUI; on Omarchy also adds a Walker
+#     entry + the Nautilus right-click integration.
+#   - Remote server (public IP): same install, then restricts port 53317 to the
+#     Tailscale interface in the firewall, so it's reachable over the tailnet
+#     only — not the open internet.
 
 set -euo pipefail
 
@@ -27,6 +31,7 @@ BIN_DIR="${BIN_DIR:-$HOME/.local/bin}"
 APP_DIR="$HOME/.local/share/applications"
 BIN="$BIN_DIR/omarchy-send"
 VERSION="${OMARCHY_SEND_VERSION:-latest}"
+PORT=53317
 
 mkdir -p "$BIN_DIR"
 
@@ -36,6 +41,30 @@ if [ -n "${BASH_SOURCE[0]:-}" ] && [ -f "${BASH_SOURCE[0]}" ]; then
   SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 fi
 
+# ---- local vs remote -----------------------------------------------------
+# A remote (public-IP) server should not expose the transfer port to the
+# internet. Ask once; default to "local" when non-interactive (e.g. piped
+# `curl | bash` with no terminal) so a firewall is never changed without intent.
+# Reads /dev/tty so the prompt still works under curl|bash.
+MODE="${OMARCHY_SEND_MODE:-}"
+case "$MODE" in
+  local | remote) : ;; # explicit override, don't ask
+  *)
+    MODE="local"
+    # Try to open the controlling terminal read-write on fd 3. A bare -r test
+    # isn't enough: /dev/tty can exist yet fail to open (no controlling tty —
+    # cron/CI/piped). Only prompt when the open actually succeeds.
+    if { exec 3<>/dev/tty; } 2>/dev/null; then
+      printf 'Install type — [L]ocal machine (home/LAN) or [r]emote server (public IP)? [L/r] ' >&3 || true
+      IFS= read -r _ans <&3 || _ans=""
+      exec 3>&- 3<&- || true
+      case "$_ans" in
+        r | R | remote | Remote | REMOTE) MODE="remote" ;;
+      esac
+    fi
+    ;;
+esac
+
 # ---- obtain the binary ---------------------------------------------------
 if [ -n "$SCRIPT_DIR" ] && [ -f "$SCRIPT_DIR/go.mod" ] && command -v go >/dev/null 2>&1; then
   echo "==> Building omarchy-send from source..."
@@ -227,6 +256,73 @@ else
   echo "==> Headless system — installed as a plain TUI."
 fi
 
+# ---- firewall posture ----------------------------------------------------
+# Shared by the remote-mode lockdown below and the local-mode public-IP warning.
+#
+# Tailscale interface: usually tailscale0, but absent when tailscaled runs in
+# userspace-networking mode (the default inside containers) — don't hardcode it.
+TS_IFACE="$(ip -o link show 2>/dev/null | grep -oE 'tailscale[0-9]+' | head -n1)"
+
+# Container? Under Docker host-networking the port binds the *host's* stack, and
+# the firewall belongs on the host, not in this namespace.
+IN_CONTAINER=0
+if [ -f /.dockerenv ] || grep -qaE 'docker|containerd|kubepods' /proc/1/cgroup 2>/dev/null; then
+  IN_CONTAINER=1
+fi
+
+# ---- remote server: restrict the port to the Tailscale network -----------
+# On a public-IP box, port 53317 would otherwise be reachable from the internet
+# (the receiver binds all interfaces). Lock it to the Tailscale interface so it
+# only answers over the tailnet. Multicast LAN discovery is link-local and never
+# routes off-LAN, so nothing else needs opening. Inside a container the firewall
+# can't be applied from here — userspace-networking has no tailscale0 and host-
+# networking puts the bind on the host's stack — so we detect that and say so.
+if [ "$MODE" = "remote" ]; then
+  echo "==> Remote server — restricting port $PORT to the Tailscale network."
+
+  if [ "$IN_CONTAINER" = "1" ] && [ -z "$TS_IFACE" ]; then
+    # Container + userspace-networking Tailscale: no tailscale0, and typically no
+    # CAP_NET_ADMIN to manage netfilter. A firewall can't be applied from in here.
+    echo "    Detected: inside a container with userspace-networking Tailscale"
+    echo "    (no tailscale0 interface). The receiver binds all interfaces — and under"
+    echo "    Docker host-networking that includes the host's PUBLIC interface."
+    echo
+    echo "    A firewall CANNOT be applied from in here. Apply it on the HOST:"
+    echo "      • if the host already default-denies inbound (e.g. only 22/80/443 open),"
+    echo "        $PORT is already blocked from the internet yet still reachable over the"
+    echo "        tailnet (tailscaled delivers it via loopback) — nothing more to do."
+    echo "      • otherwise, on the host run:  ufw deny $PORT"
+    echo "    Strongly recommended in this setup: also set a PIN (--pin <code>)."
+  elif [ -n "$TS_IFACE" ] && command -v ufw >/dev/null 2>&1; then
+    SUDO=""
+    [ "$(id -u)" -ne 0 ] && SUDO="sudo"
+    echo "    Tailscale interface: $TS_IFACE"
+    echo "    Applying firewall rules (may prompt for sudo):"
+    echo "      ${SUDO:+$SUDO }ufw allow in on $TS_IFACE to any port $PORT"
+    echo "      ${SUDO:+$SUDO }ufw deny $PORT"
+    if $SUDO ufw allow in on "$TS_IFACE" to any port "$PORT" >/dev/null 2>&1 &&
+      $SUDO ufw deny "$PORT" >/dev/null 2>&1; then
+      echo "    Done — $PORT answers over Tailscale only."
+    else
+      echo "    Could not apply automatically (need root/sudo). Run the two commands above yourself."
+    fi
+  else
+    if [ -z "$TS_IFACE" ]; then
+      echo "    NOTE: no tailscale interface found. If tailscale isn't up yet, install it"
+      echo "          and run 'tailscale up', then re-run this installer. If it's running"
+      echo "          in userspace-networking mode, firewall the port on the host instead."
+      TS_IFACE="tailscale0"
+    fi
+    echo "    ufw not found. Apply the equivalent in your firewall:"
+    echo "      • allow inbound TCP $PORT only on the '$TS_IFACE' interface"
+    echo "      • deny inbound $PORT on all other interfaces"
+    echo "    nftables example (inet filter, input chain):"
+    echo "      iifname \"$TS_IFACE\" tcp dport $PORT accept"
+    echo "      tcp dport $PORT drop"
+  fi
+  echo "    Tip: a PIN adds a second layer — run with --pin <code> (or set it in Settings)."
+fi
+
 echo
 case ":$PATH:" in
   *":$BIN_DIR:"*) : ;;

internal/config/config.go

@@ -25,6 +25,11 @@ type Config struct {
 	NoIcons     bool   `json:"noIcons"`  // hide Nerd Font device icons (non-NF terminals)
 	NoNotify    bool   `json:"noNotify"` // don't raise desktop notifications on incoming messages/files
 
+	// KnownPeers are hosts (name, IP, or host:port) probed directly over unicast
+	// so peers off the local subnet — e.g. reached over Tailscale — show up even
+	// though multicast discovery can't find them.
+	KnownPeers []string `json:"knownPeers,omitempty"`
+
 	// TLS identity for encrypted (HTTPS) mode, generated once and persisted.
 	CertPEM string `json:"certPem"`
 	KeyPEM  string `json:"keyPem"`

internal/discovery/discovery.go

@@ -295,6 +295,61 @@ func (d *Discoverer) reply(ip string, port int, proto string) {
 	_ = resp.Body.Close()
 }
 
+// Probe contacts host directly over unicast — bypassing multicast — and records
+// it as a peer on success. It POSTs our info to the peer's /register (so the
+// peer also learns us) and reads the peer's info from the reply. host may carry
+// a port; otherwise the default LocalSend port is used. https is tried first,
+// then http. Used for known/remote peers (e.g. reached over Tailscale) that
+// multicast can't find. Re-probing a live peer refreshes its LastSeen so it is
+// not reaped; a peer that stops answering ages out normally.
+func (d *Discoverer) Probe(ctx context.Context, host string) error {
+	h, port := hostPort(host)
+	body, err := json.Marshal(d.selfCopy().WithAnnounce(false))
+	if err != nil {
+		return err
+	}
+	var lastErr error
+	for _, scheme := range []string{"https", "http"} {
+		url := fmt.Sprintf("%s://%s/api/localsend/v2/register", scheme, net.JoinHostPort(h, strconv.Itoa(port)))
+		req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(body))
+		if err != nil {
+			return err
+		}
+		req.Header.Set("Content-Type", "application/json")
+		resp, err := d.client.Do(req)
+		if err != nil {
+			lastErr = err
+			continue
+		}
+		var info protocol.DeviceInfo
+		derr := json.NewDecoder(resp.Body).Decode(&info)
+		_ = resp.Body.Close()
+		if derr != nil || info.Fingerprint == "" {
+			lastErr = fmt.Errorf("probe %s: no usable device info", url)
+			continue
+		}
+		dbg.Logf("probe %s -> alias=%q fp=%s", url, info.Alias, info.Fingerprint)
+		d.NotePeer(info, h) // reach it back at the host we dialed
+		return nil
+	}
+	if lastErr == nil {
+		lastErr = fmt.Errorf("could not reach %s", host)
+	}
+	return lastErr
+}
+
+// hostPort splits an optional :port off host, defaulting to the LocalSend port.
+// It handles bare IPv6 by requiring the [::]:port form for a custom port.
+func hostPort(host string) (string, int) {
+	if h, p, err := net.SplitHostPort(host); err == nil {
+		if n, err := strconv.Atoi(p); err == nil {
+			return h, n
+		}
+		return h, protocol.DefaultPort
+	}
+	return host, protocol.DefaultPort
+}
+
 // NotePeer records a peer (from multicast or from an inbound /register) and
 // emits PeerFound on first sight or when its address changes. Safe for
 // concurrent use; ignores our own fingerprint.

internal/discovery/probe_test.go

@@ -0,0 +1,64 @@
+package discovery
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"omarchy-send/internal/protocol"
+)
+
+// TestProbeRegistersPeer drives Probe against a stub /register that behaves like
+// a real peer: it records the caller and returns its own DeviceInfo. The https
+// attempt fails against the plain-http test server and Probe falls back to http.
+func TestProbeRegistersPeer(t *testing.T) {
+	peerInfo := protocol.DeviceInfo{Alias: "Remote", Fingerprint: "remote-fp", Port: 53317, Protocol: "http"}
+	var sawOurInfo bool
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/api/localsend/v2/register", func(w http.ResponseWriter, r *http.Request) {
+		var in protocol.DeviceInfo
+		if err := json.NewDecoder(r.Body).Decode(&in); err == nil && in.Fingerprint == "self-fp" {
+			sawOurInfo = true
+		}
+		_ = json.NewEncoder(w).Encode(peerInfo)
+	})
+	srv := httptest.NewServer(mux)
+	defer srv.Close()
+	host := strings.TrimPrefix(srv.URL, "http://") // host:port
+
+	d := New(protocol.DeviceInfo{Fingerprint: "self-fp", Alias: "Self"})
+	if err := d.Probe(context.Background(), host); err != nil {
+		t.Fatalf("Probe failed: %v", err)
+	}
+	if !sawOurInfo {
+		t.Error("peer did not receive our device info in the register body")
+	}
+	peers := d.Snapshot()
+	if len(peers) != 1 || peers[0].Info.Fingerprint != "remote-fp" {
+		t.Fatalf("peer not recorded as expected: %+v", peers)
+	}
+	if wantIP := strings.Split(host, ":")[0]; peers[0].IP != wantIP {
+		t.Errorf("peer IP = %q, want %q (the host we dialed)", peers[0].IP, wantIP)
+	}
+}
+
+func TestProbeUnreachableErrors(t *testing.T) {
+	d := New(protocol.DeviceInfo{Fingerprint: "self-fp"})
+	// 127.0.0.1:1 — nothing listening; both https and http should fail fast.
+	if err := d.Probe(context.Background(), "127.0.0.1:1"); err == nil {
+		t.Fatal("expected an error probing an unreachable host")
+	}
+}
+
+func TestHostPortDefaults(t *testing.T) {
+	if h, p := hostPort("colossus"); h != "colossus" || p != protocol.DefaultPort {
+		t.Errorf("hostPort(bare) = %q,%d; want colossus,%d", h, p, protocol.DefaultPort)
+	}
+	if h, p := hostPort("100.64.0.2:9999"); h != "100.64.0.2" || p != 9999 {
+		t.Errorf("hostPort(host:port) = %q,%d; want 100.64.0.2,9999", h, p)
+	}
+}

internal/tailscale/tailscale.go

@@ -0,0 +1,77 @@
+// Package tailscale discovers peer addresses from a local Tailscale daemon, so
+// omarchy-send can reach devices that share a tailnet but not a LAN subnet (and
+// therefore can't be found by multicast). It shells out to the `tailscale` CLI
+// and is a no-op when that isn't present.
+package tailscale
+
+import (
+	"context"
+	"encoding/json"
+	"os/exec"
+)
+
+// status is the subset of `tailscale status --json` we care about.
+type status struct {
+	Peer map[string]struct {
+		TailscaleIPs []string `json:"TailscaleIPs"`
+		Online       bool     `json:"Online"`
+	} `json:"Peer"`
+}
+
+// Available reports whether the tailscale CLI is on PATH.
+func Available() bool {
+	_, err := exec.LookPath("tailscale")
+	return err == nil
+}
+
+// Peers returns the IPv4 Tailscale address of each online peer in the tailnet.
+// It returns nil (no error) when tailscale isn't installed, isn't running, or
+// the output can't be parsed — callers treat Tailscale discovery as best-effort.
+func Peers(ctx context.Context) []string {
+	if !Available() {
+		return nil
+	}
+	out, err := exec.CommandContext(ctx, "tailscale", "status", "--json").Output()
+	if err != nil {
+		return nil
+	}
+	return parsePeers(out)
+}
+
+// parsePeers extracts each online peer's first IPv4 address from the JSON of
+// `tailscale status --json`. Split out so it can be tested without the CLI.
+func parsePeers(data []byte) []string {
+	var st status
+	if err := json.Unmarshal(data, &st); err != nil {
+		return nil
+	}
+	var hosts []string
+	for _, p := range st.Peer {
+		if !p.Online {
+			continue
+		}
+		for _, ip := range p.TailscaleIPs {
+			if isIPv4(ip) {
+				hosts = append(hosts, ip)
+				break // one address per peer is enough to probe
+			}
+		}
+	}
+	return hosts
+}
+
+// isIPv4 reports whether s looks like a dotted-quad (cheap check — avoids
+// pulling in net just to skip the IPv6 entries Tailscale also reports).
+func isIPv4(s string) bool {
+	dots := 0
+	for _, c := range s {
+		switch {
+		case c == '.':
+			dots++
+		case c >= '0' && c <= '9':
+		default:
+			return false
+		}
+	}
+	return dots == 3
+}

internal/tailscale/tailscale_test.go

@@ -0,0 +1,46 @@
+package tailscale
+
+import (
+	"reflect"
+	"sort"
+	"testing"
+)
+
+func TestParsePeersOnlineIPv4Only(t *testing.T) {
+	data := []byte(`{
+		"Peer": {
+			"key1": {"TailscaleIPs": ["100.64.0.1", "fd7a:115c::1"], "Online": true},
+			"key2": {"TailscaleIPs": ["100.64.0.2"], "Online": false},
+			"key3": {"TailscaleIPs": ["fd7a:115c::3"], "Online": true},
+			"key4": {"TailscaleIPs": ["100.64.0.4"], "Online": true}
+		}
+	}`)
+	got := parsePeers(data)
+	sort.Strings(got)
+	want := []string{"100.64.0.1", "100.64.0.4"} // online + has IPv4; offline and v6-only excluded
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("parsePeers = %v, want %v", got, want)
+	}
+}
+
+func TestParsePeersBadJSON(t *testing.T) {
+	if got := parsePeers([]byte("not json")); got != nil {
+		t.Errorf("bad JSON should yield nil, got %v", got)
+	}
+}
+
+func TestIsIPv4(t *testing.T) {
+	cases := map[string]bool{
+		"100.64.0.1":   true,
+		"1.2.3.4":      true,
+		"fd7a:115c::1": false,
+		"1.2.3":        false,
+		"":             false,
+		"abc":          false,
+	}
+	for in, want := range cases {
+		if got := isIPv4(in); got != want {
+			t.Errorf("isIPv4(%q) = %v, want %v", in, got, want)
+		}
+	}
+}

internal/tui/model.go

@@ -38,6 +38,7 @@ type Controller interface {
 	SetReceiveDir(string)
 	SetPIN(string)
 	SetNotify(bool)
+	AddKnownPeer(host string) // probe a remote host directly (off-LAN / Tailscale)
 }
 
 type screen int
@@ -123,6 +124,10 @@ type Model struct {
 	sendPaths  []string
 	pendingMsg string
 
+	// Add-remote-peer modal (Devices tab): host/IP/Tailscale-name entry.
+	addingPeer bool
+	peerInput  textinput.Model
+
 	// Messages tab + compose modal.
 	msgList      list.Model
 	messages     []server.ReceivedMessage
@@ -199,6 +204,11 @@ func New(cfg config.Config, ctrl Controller, opts ...Option) Model {
 	compose.CharLimit = 2000
 	compose.Width = 48
 
+	peerInput := textinput.New()
+	peerInput.Placeholder = "host, IP, or Tailscale name"
+	peerInput.CharLimit = 256
+	peerInput.Width = 48
+
 	mkInput := func(placeholder string, limit int) textinput.Model {
 		ti := textinput.New()
 		ti.Placeholder = placeholder
@@ -229,6 +239,7 @@ func New(cfg config.Config, ctrl Controller, opts ...Option) Model {
 		editInputs:   editInputs,
 		msgList:      ml,
 		composeInput: compose,
+		peerInput:    peerInput,
 	}
 	for _, o := range opts {
 		o(&m)
@@ -321,6 +332,9 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		if m.composing {
 			return m.updateCompose(msg)
 		}
+		if m.addingPeer {
+			return m.updateAddPeer(msg)
+		}
 		if m.readingMsg != nil {
 			switch msg.String() {
 			case "esc", "q", "enter":
@@ -387,6 +401,15 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				m.refreshManage()
 			}
 			return m, nil
+		case "+":
+			// Add a remote device by host/IP/Tailscale-name (off-LAN peer).
+			if m.screen == screenPeers {
+				m.addingPeer = true
+				m.peerInput.SetValue("")
+				m.peerInput.Focus()
+				return m, textinput.Blink
+			}
+			return m, nil
 		case "r":
 			if m.screen == screenPeers && m.ctrl != nil {
 				m.ctrl.Announce()
@@ -547,6 +570,11 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		}
 	}
 
+	if m.addingPeer {
+		var cmd tea.Cmd
+		m.peerInput, cmd = m.peerInput.Update(msg)
+		return m, cmd
+	}
 	if m.pending == nil && m.screen == screenPicker {
 		var cmd tea.Cmd
 		m.fzfQuery, cmd = m.fzfQuery.Update(msg)
@@ -597,6 +625,33 @@ func (m Model) updateCompose(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 	return m, cmd
 }
 
+// updateAddPeer handles the add-remote-device modal. On enter it persists the
+// host to config's known-peers and asks the controller to probe it now.
+func (m Model) updateAddPeer(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
+	switch msg.String() {
+	case "esc":
+		m.addingPeer = false
+		return m, nil
+	case "enter":
+		host := strings.TrimSpace(m.peerInput.Value())
+		if host != "" {
+			if !contains(m.cfg.KnownPeers, host) {
+				m.cfg.KnownPeers = append(m.cfg.KnownPeers, host)
+				_ = m.cfg.Save()
+			}
+			if m.ctrl != nil {
+				m.ctrl.AddKnownPeer(host)
+			}
+			m.notice = "added remote " + host + " — probing…"
+		}
+		m.addingPeer = false
+		return m, nil
+	}
+	var cmd tea.Cmd
+	m.peerInput, cmd = m.peerInput.Update(msg)
+	return m, cmd
+}
+
 // deleteSelectedMessage drops the highlighted message from the list.
 func (m *Model) deleteSelectedMessage() {
 	it, ok := m.msgList.SelectedItem().(msgItem)
@@ -848,6 +903,9 @@ func (m Model) View() string {
 	if m.composing {
 		return lipgloss.Place(w, h, lipgloss.Center, lipgloss.Center, cardStyle.Render(m.composeView()))
 	}
+	if m.addingPeer {
+		return lipgloss.Place(w, h, lipgloss.Center, lipgloss.Center, cardStyle.Render(m.addPeerView()))
+	}
 	if m.readingMsg != nil {
 		return lipgloss.Place(w, h, lipgloss.Center, lipgloss.Center, cardStyle.Render(m.readMessageView()))
 	}
@@ -984,6 +1042,18 @@ func (m Model) pinView() string {
 	return b.String()
 }
 
+func (m Model) addPeerView() string {
+	var b strings.Builder
+	b.WriteString(titleStyle.Render("Add remote device"))
+	b.WriteString("\n\n")
+	b.WriteString(headerStyle.Render("A device off your LAN — e.g. a Tailscale name or IP.\nIt's probed directly (no multicast) and saved."))
+	b.WriteString("\n\n")
+	b.WriteString(m.peerInput.View())
+	b.WriteString("\n\n")
+	b.WriteString(footerStyle.Render("enter add · esc cancel"))
+	return b.String()
+}
+
 func (m Model) acceptView() string {
 	var b strings.Builder
 	b.WriteString(titleStyle.Render("Incoming files"))
@@ -1233,6 +1303,8 @@ func (m Model) footerText() string {
 		return m.notice
 	case m.composing:
 		return "enter send · esc cancel"
+	case m.addingPeer:
+		return "enter add remote · esc cancel"
 	case m.readingMsg != nil:
 		return "y copy · esc/enter close"
 	case m.confirmDel:
@@ -1244,7 +1316,7 @@ func (m Model) footerText() string {
 	case m.screen == screenPeers && m.quickSend:
 		return fmt.Sprintf("enter send %d item(s) to selected device · r refresh · q cancel", len(m.staged))
 	case m.screen == screenPeers:
-		return "enter send-to · m message · v send-clipboard · r refresh · / filter · 1-5 · q quit"
+		return "enter send-to · m message · v clipboard · + add remote · r refresh · / filter · q quit"
 	case m.screen == screenTransfers:
 		return "c clear finished · 1-5 switch · q quit"
 	case m.screen == screenManage:

internal/tui/send_test.go

@@ -33,6 +33,7 @@ func (f *fakeCtrl) SetAlias(string)                                {}
 func (f *fakeCtrl) SetReceiveDir(string)                           {}
 func (f *fakeCtrl) SetPIN(string)                                  {}
 func (f *fakeCtrl) SetNotify(bool)                                 {}
+func (f *fakeCtrl) AddKnownPeer(string)                            {}
 
 // writeTree lays out a small fixture tree under a temp dir for walkIndex tests.
 func writeTree(t *testing.T) string {