they look like transparent leds or black leds,3 pins, from 5 to 20 mm, depending on range, this is what i found out from someone that works at an alarm company, but i think it is quite hard to find them as components....
2 bad i needed them too.
but i dont thing that you can use an IR led, because it will sense ambient light and any sourcce of heat, even a flashlight, or even a key chain laser, but i dont think deers use lasers
:lol:
an alternative is to make an oscilator, LC, and attach a long wire to the "hot" wire, the connection from the cap and the coil and someone going around the wire will caouse the osc to stop oscilating or change the frequency, wich will cause the trigger.
you will probably ask me how to do this...well, i dont know, i just know the theory.
if i remember well i have something like this in a book, but it is very old, with Ge transistors, and you have to make the coil yourself....
1 turn, 2 turns, 3 turns.........
you get the idea, ill search the 'net for more.