Guard2 runs silently on an Android device and sends you an email alert when that device goes offline or stays inactive during the day (night hours 23:00–07:00 don't count) — a lightweight device-activity monitoring tool. No accounts, no complexity.
Looking for a Demumu alternative? Guard2 is the simpler, no-check-in choice. It just runs. It just notifies.
Keep a quiet eye on whether a device is active and reachable — a lightweight activity-monitoring tool, not surveillance.
Check that a family member's device is still active during the day. No wearable needed — just their regular smartphone.
College students or children away from home. Know their device is active without texting them every few hours.
Different time zones make it hard to stay in sync. Guard2 bridges the gap — you'll know if a device goes inactive before you even wake up.
Hiking, road trips, remote locations. If the device goes dark, your designated contact gets a notification so they know to check in.
Monitor multiple devices from a single email inbox. Each device sends notifications independently, so you always know which one is inactive.
Some people simply don't respond to messages. Guard2 tells you their device is alive and active — that alone is peace of mind.
Install once, configure in under a minute, then forget about it. Guard2 runs quietly in the background — you only hear from it when something is wrong.
Install Guard2 via the Google Play test on the device you want to monitor (a family member's phone, a parent's tablet, etc.). Joining the test requires a Google Play account — email weiheerlai@163.com to request access.
Give the device a recognizable name (e.g. "Dad's Phone") and enter the email addresses that should receive alerts. No account creation required.
The background service and scheduled task keep running continuously, sending a heartbeat every 20 minutes. Protection continues reliably even with the screen locked or app in the background, with minimal battery impact.
If no heartbeat is received for 2+ hours, or the screen hasn't been unlocked in 6+ hours, all designated recipients get an alert email instantly. These thresholds count only daytime hours — the device's local night window (23:00–07:00) is excluded from the count, so overnight inactivity never triggers a false alarm.
As soon as the device comes back online or the screen is unlocked, a recovery notification is sent — so you're never left wondering.
Guard2 is intentionally minimal — built to do one thing extremely well.
Automatic heartbeat every 20 minutes, survives screen lock, app kill, and device restart.
Detects whether someone physically unlocked the device in the last 30-minute window.
Alert up to 3 email addresses simultaneously. All recipients receive every alert type independently.
When the situation resolves — device comes back online, screen is unlocked — everyone is notified right away.
When your subscription expires, monitoring stops automatically and a notification is sent. Settings are safely preserved for quick renewal.
No location data. No contacts. No media. Only a random device ID, a nickname, and your chosen email addresses.
No server to manage. No account to create. The backend is fully managed — just install and start.
Monitor multiple devices using the same recipient email. Each device has its own nickname for easy identification.
| Type | Trigger | Subject Line |
|---|---|---|
| ⚠️ Heartbeat Alert | No heartbeat for >2 hours | [Guard2 Alert] Device "…" is inactive |
| ⚠️ Unlock Alert | Screen not unlocked for >6 hours | [Guard2 Alert] Device "…" is inactive |
| 💚 Heartbeat Recovery | Heartbeat resumes after alert | [Guard2 Recovery] Device "…" heartbeat restored |
| 🔓 Unlock Recovery | Screen unlocked after alert | [Guard2 Recovery] Device "…" screen unlocked |
| ✓ Monitoring Started | User taps START | [Guard2] Device "…" monitoring started |
| ■ Monitoring Stopped | User taps STOP, or subscription expires (auto-stopped) | [Guard2] Device "…" monitoring stopped / (subscription expired) |