Purpose: to create a cheap, effective and simple wireless alarm system using pre-existing hardware, reducing $$$…
Description: This setup utilizes a Bluetooth headphone (earpiece headset should also work), a song playing on infinite loop, computer that’s paired with the Bluetooth headset (my OS: Ubuntu 10.04) and external speakers and a metal box.
How it works: the principle behind this alarm system is that the music is played through the Bluetooth headphone/earpiece until the 2.4Ghz signal coming from the laptop is severed (ex: metal box closes), upon which the computer automatically switches to external speakers to play the sound. The interruption of the Bluetooth signal is what activates the alarm.
Uses: The sky’s the limit on how this principle is used. One example could be a mouse trap - Mouse triggers mousetrap, which closes a metal box around the bluetooth headset, alerting the computer the connection’s been disconnected.
How is this better than a wire and a buzzer? It’s wireless! Although the battery on the earpiece/headset may die after a couple hours, it shouldn’t be too hard to crack open a cheap one and solder on a lead to add a larger battery pack.
Caviats: range - (with stock antennas) are good for maybe 10ft, or a little more. If you hack the antenna it can go much farther (50+ft depending)
Reliability - computer setup would have to be always on, always connected. Bluetooth connections aren’t always the most reliable setup.