diff --git a/.env.example b/.env.example
index 1e8f58b..5fb7d49 100644
--- a/.env.example
+++ b/.env.example
@@ -16,6 +16,12 @@ SELF_HOSTED=true
 # who want to be notified of signups set this to their own address.
 # ADMIN_NOTIFY_EMAIL=you@example.com
 
+# Marks THIS deployment as the hosted (screentinker.com) instance. Gates the
+# daily activation-nudge sweep (the T+3 "haven't paired a screen yet?" email).
+# Leave UNSET on self-hosted instances so a daily bulk sweep never emails your
+# user base with our onboarding mail. Only the hosted instance sets this true.
+# HOSTED_INSTANCE=true
+
 # --- Outbound email (Microsoft Graph, client-credentials flow) ---
 # Required for ANY email (welcome, offline alerts, admin notify) to actually
 # send. Leave blank and the app logs "[EMAIL] not configured" instead of sending.
diff --git a/server/db/database.js b/server/db/database.js
index 902da80..4247e09 100644
--- a/server/db/database.js
+++ b/server/db/database.js
@@ -153,6 +153,15 @@ const migrations = [
   // sent at <time>". The backfill is idempotent: re-runs match nothing.
   "ALTER TABLE users ADD COLUMN welcome_email_sent_at INTEGER",
   "UPDATE users SET welcome_email_sent_at = 1 WHERE welcome_email_sent_at IS NULL",
+  // Slice 3: idempotency guard for the one-time T+3 activation nudge. Same
+  // shape as welcome_email_sent_at: non-null = handled. New signups get a real
+  // unix-seconds stamp when the daily sweep emails them (see
+  // services/activationNudge.js). The paired sentinel-1 backfill marks every
+  // pre-existing user as handled so the FIRST sweep can't blast the entire
+  // dormant legacy base with a stale "you signed up a few days ago" nudge --
+  // only genuinely-new signups (NULL) become eligible going forward.
+  "ALTER TABLE users ADD COLUMN activation_nudge_sent_at INTEGER",
+  "UPDATE users SET activation_nudge_sent_at = 1 WHERE activation_nudge_sent_at IS NULL",
 ];
 for (const sql of migrations) {
   try { db.exec(sql); } catch (e) { /* already exists */ }
diff --git a/server/server.js b/server/server.js
index 63e9c78..fb3eeae 100644
--- a/server/server.js
+++ b/server/server.js
@@ -491,6 +491,10 @@ startScheduler(io);
 const { startAlertService } = require('./services/alerts');
 startAlertService(io);
 
+// Start activation-nudge sweep (T+3 onboarding nudge; gated on HOSTED_INSTANCE)
+const { startActivationNudge } = require('./services/activationNudge');
+startActivationNudge();
+
 // Handle provisioning via WebSocket notification
 const { db } = require('./db/database');
 const originalProvisionRoute = require('./routes/provisioning');
diff --git a/server/services/activationNudge.js b/server/services/activationNudge.js
new file mode 100644
index 0000000..eba1786
--- /dev/null
+++ b/server/services/activationNudge.js
@@ -0,0 +1,155 @@
+// Activation nudge (Slice 3): a once-per-user "checking in" email sent T+3 days
+// after signup when the user still has zero paired screens. Daily sweep at a
+// fixed UTC hour. Reuses the single Microsoft Graph transport (./email).
+//
+// GATING — positive hosted signal, NOT !selfHosted:
+//   This is a daily BULK sweep. A self-hoster who configured Graph but forgot
+//   SELF_HOSTED=true would blast their whole dormant user base with Dan-branded
+//   onboarding mail. So we gate on an explicit HOSTED_INSTANCE=true: if it's not
+//   set, we neither schedule nor send. Hosted prod sets the env var.
+//
+// Idempotency: users.activation_nudge_sent_at, stamped after each send; the
+// query's "IS NULL" guard means a user is nudged at most once. Re-runs are safe.
+//
+// Opt-out: users who explicitly turned email alerts off (email_alerts = 0) are
+// excluded; NULL/unset and on (1) both qualify via COALESCE(...,1)=1.
+
+const { db } = require('../db/database');
+const { sendEmail } = require('./email');
+
+const NUDGE_HOUR_UTC = 15; // 15:00 UTC daily
+
+const LINKS = {
+  player:     'https://screentinker.com/player/',
+  pi:         'https://screentinker.com/guides/raspberry-pi-digital-signage.html',
+  androidTv:  'https://screentinker.com/guides/digital-signage-android-tv.html',
+  selfHosted: 'https://screentinker.com/guides/self-hosted-digital-signage.html',
+  discord:    'https://discord.gg/utTdsrqq4Z',
+};
+
+function htmlEscape(s) {
+  return String(s).replace(/[&<>"']/g, c =>
+    ({ '&':'&amp;','<':'&lt;','>':'&gt;','"':'&quot;',"'":'&#39;' }[c]));
+}
+
+// Pure-ASCII plain text (same deliverability rule as the welcome email).
+function nudgeText(name) {
+  return `Hi ${name},
+
+You signed up for ScreenTinker a few days ago, and I noticed you
+haven't paired a screen yet. No worries at all. I just wanted to
+check in and see if anything's getting in the way.
+
+If you hit a snag, hit reply and tell me what happened. It comes
+straight to me and I'll help you sort it.
+
+If you just haven't had a chance yet, the fastest way to start is the
+web player. Turn any browser into a screen in about a minute:
+
+  -> ${LINKS.player}
+
+Or if you're setting up real hardware:
+  - Raspberry Pi: ${LINKS.pi}
+  - Android TV:   ${LINKS.androidTv}
+  - Self-hosted:  ${LINKS.selfHosted}
+
+And the Discord is here if you'd rather ask there:
+  ${LINKS.discord}
+
+And if you'd rather I didn't check in, just say the word.
+
+- Dan
+ScreenTinker`;
+}
+
+function nudgeHtml(name) {
+  return `<div style="font-family:-apple-system,'Segoe UI',Roboto,sans-serif;font-size:15px;line-height:1.6;color:#222;max-width:560px">
+<p>Hi ${htmlEscape(name)},</p>
+<p>You signed up for ScreenTinker a few days ago, and I noticed you haven't paired a screen yet. No worries at all. I just wanted to check in and see if anything's getting in the way.</p>
+<p>If you hit a snag, hit reply and tell me what happened. It comes straight to me and I'll help you sort it.</p>
+<p>If you just haven't had a chance yet, the fastest way to start is the web player. Turn any browser into a screen in about a minute:</p>
+<p><a href="${LINKS.player}" style="font-weight:600">Open the web player</a></p>
+<p>Or if you're setting up real hardware:</p>
+<ul>
+  <li><a href="${LINKS.pi}">Raspberry Pi setup</a></li>
+  <li><a href="${LINKS.androidTv}">Android TV setup</a></li>
+  <li><a href="${LINKS.selfHosted}">Self-hosted setup</a></li>
+</ul>
+<p>And the <a href="${LINKS.discord}">Discord is here</a> if you'd rather ask there.</p>
+<p>And if you'd rather I didn't check in, just say the word.</p>
+<p>- Dan<br>ScreenTinker</p>
+</div>`;
+}
+
+// Eligible = signed up 3-14 days ago, never nudged, not opted out, and with
+// ZERO devices either owned by the user OR present in any workspace they belong
+// to (Option B, workspace-aware — avoids nudging engaged team members).
+const ELIGIBLE_SQL = `
+  SELECT u.id, u.email, u.name FROM users u
+  WHERE u.created_at < strftime('%s','now') - (3 * 86400)
+    AND u.created_at > strftime('%s','now') - (14 * 86400)
+    AND u.activation_nudge_sent_at IS NULL
+    AND COALESCE(u.email_alerts, 1) = 1
+    AND NOT EXISTS (SELECT 1 FROM devices d WHERE d.user_id = u.id)
+    AND NOT EXISTS (
+      SELECT 1 FROM workspace_members wm
+      JOIN devices d2 ON d2.workspace_id = wm.workspace_id
+      WHERE wm.user_id = u.id)
+`;
+
+function isHosted() {
+  return process.env.HOSTED_INSTANCE === 'true';
+}
+
+// Run one sweep. Exported so the dev verify harness can drive it directly
+// without waiting for 15:00 UTC. Returns the number of nudges sent.
+async function runActivationNudgeSweep() {
+  if (!isHosted()) return 0; // defense in depth (scheduler is also gated)
+  const users = db.prepare(ELIGIBLE_SQL).all();
+  console.log(`[NUDGE] sweep: ${users.length} eligible user(s)`);
+  let sent = 0;
+  for (const u of users) {
+    const name = (u.name && u.name.trim()) ? u.name.trim() : u.email.split('@')[0];
+    const r = await sendEmail({
+      to: u.email,
+      fromName: 'Dan at ScreenTinker',
+      rawSubject: true,
+      subject: "Quick check-in - how's ScreenTinker going?",
+      text: nudgeText(name),
+      html: nudgeHtml(name),
+    });
+    console.log(`[NUDGE] nudge -> ${u.email}: ${JSON.stringify(r)}`);
+    // Stamp after the send (no retry, same discipline as the welcome email).
+    db.prepare("UPDATE users SET activation_nudge_sent_at = strftime('%s','now') WHERE id = ?").run(u.id);
+    sent++;
+  }
+  return sent;
+}
+
+function msUntilNextRun() {
+  const now = new Date();
+  const next = new Date(Date.UTC(
+    now.getUTCFullYear(), now.getUTCMonth(), now.getUTCDate(), NUDGE_HOUR_UTC, 0, 0, 0));
+  if (next.getTime() <= now.getTime()) next.setUTCDate(next.getUTCDate() + 1);
+  return next.getTime() - now.getTime();
+}
+
+// Self-correcting daily scheduler (recompute next 15:00 UTC each run; no drift,
+// no node-cron dependency). Gated on HOSTED_INSTANCE.
+function startActivationNudge() {
+  if (!isHosted()) {
+    console.log('[NUDGE] HOSTED_INSTANCE not set - activation nudge sweep disabled');
+    return;
+  }
+  const schedule = () => {
+    const delay = msUntilNextRun();
+    console.log(`[NUDGE] next activation-nudge sweep in ~${Math.round(delay / 60000)} min (15:00 UTC daily)`);
+    setTimeout(() => {
+      runActivationNudgeSweep().catch(e => console.error('[NUDGE] sweep error:', e.message));
+      schedule();
+    }, delay);
+  };
+  schedule();
+}
+
+module.exports = { startActivationNudge, runActivationNudgeSweep };