Distance alarm circuit

Thread Starter

jr1964

Joined Mar 17, 2009
1
I'll describe what I'm looking for since I'm not sure what the correct name would be, or if it even exists:

a) I have a static base
b) I have a portable transmitter
c) When (a) is more than xxx feet from (b), an alarm will sound.

Both components should be small and portable and the effective distance should not be more that 30~50 yards.

Any ideas?
 
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