It doesn't have to be a digital camera, when I was a TV tech it was standard practice to operate and point the remote control towards a standard home video camera, the infra red emitter would show up on the monitor/TV.
Prior to infra red remote controls it was ultrasonic using an electronic transducer, prior to that it was the old pinger, any old techs remember the pinger, murphy used to use them as I remember, long after they became defunct and the technology had moved on some customers still referred to the remote control as the pinger, at least around the Manchester area anyways.
Lawrence.
Edit: Maybe photo cells were used as well earlier on? can't quite remember.
Prior to infra red remote controls it was ultrasonic using an electronic transducer, prior to that it was the old pinger, any old techs remember the pinger, murphy used to use them as I remember, long after they became defunct and the technology had moved on some customers still referred to the remote control as the pinger, at least around the Manchester area anyways.
Lawrence.
Edit: Maybe photo cells were used as well earlier on? can't quite remember.
