I am currently attempting to build a proximity alarm that would ideally go off at somewhere between 5 and 20 meters.
The main requirement is that it must work through walls and barriers, which according to my research is very difficult to achieve. I would like for there to be one main unit and another 'beacon' unit.
I understand that methods such as ultrasonic and IR distsance sensors are relatively simple, i am currently at a loss to find a suitable method, having researched bluetooth, to no avail, it seems as though the pairing process would simply be too slow...
I have an arduino uno, but if any others would be more suitable, please let me know... Has anyone built something like this, or does anyone have any ideas on how it might work?? Any help is much appreciated!! :)