need help new to electronics have idea

[ploppybax]

Hi all,
what iam looking for is some circuit ideas for a system that alerts me when an object is say, 2 meters from the detector, i was thinking of some sort of RF generator that 'missed' a signal when the 2 meters distance was made, causing the detector to alert.
the transmitter as such needs to be powerless? is this possible, i know that it can be done with car ignition systems where the voltage is induced into the coil...can the transmitter store a small charge when close to the detector then when its out of range set the detector off.
I hope i am getting my idea across please help!! any ideas will do...

 

[audioguru2]

Hi Ploppy,
Welcome to our forum. ;D
Stores anti-theft systems use a powerless tuned circuit of a printed metalic coil with some stray capacitance as a proximity detector. Their sensors near the doorways seem to be huge and their range isn't 2m.
For your transmitter to be powered when close and store a charge to keep transmitting when at a distance of less than 2m would require them to have an expensive super-cap or rechargable battery.