You could use an IR remote control receiver. It will detect IR that is modulated at about 38 kHz. You could use one Arduino (even a very small one like a Nano) send out a short 38 kHz pulse a few times a second.
You could use an IR remote control receiver. It will detect IR that is modulated at about 38 kHz. You could use one Arduino (even a very small one like a Nano) send out a short 38 kHz pulse a few times a second.