Bluetooth belt buckle / broach?
How about a small, rechargeable Bluetooth device that serves no purpose other than to keep your smartphone, tablet or laptop unlocked when said device is within range? You could even use it in 'pub' mode where when the device goes out of range you get an audible warning. Maybe the device could have its own buzzer to alert you when the connected devices drop out of range?
Biting the hand that feeds IT
