tell me about the cheapest proximity detector?

the_lane8 years ago
I just clicked the link lol.
jtobako8 years ago
Your hand. Price-free/original equipment, range-about 3 feet/1 meter... Care to put some limits on your question? A therimin will 'detect' someone by their capacitance and emit a range of tones depending on how close they are. There are several IR light switches on the market at about $30? and up. You could put a microphone on the ground and amplify the sound of footsteps.