Bluetooth Anti-Lost Device, also known as Smart Bluetooth Anti-Lost Device, features a simple and lightweight design for easy portability. It operates by detecting changes in distance to determine if the item is still within your safe range. If the target exceeds the safe zone, both the phone and the anti-lost device will sound an alarm simultaneously.

Two-way Anti-loss Tracking: If the relative distance between the phone and this device exceeds the warning range, an alarm will sound immediately. You can also locate the item through the phone or find the phone through this device.

Powerful and stable performance: Features adjustable distance (0-50 meters), anti-loss, find, alarm prompt (or with vibration function), automatic power-saving, and utilizes advanced AES128 encoding technology for reliable and stable performance.

From the above content, it appears that the design principle of the Bluetooth 5.1 anti-loss device is just that, and then by installing the app software on your phone and performing some simple settings and pairing, the anti-loss feature can be activated.