[red-dawg]

That ultrasonic remote was fun to play with. We would jingle our keys in front of the TV and the channel would change.

[HiTech RedNeck]

The sound made by the plug on the end of an antenna cable when it (gently) hit the glass screen of the TV could also make the remote sensor do things, at the TV shop where I had a summer job before I went to college.

The first ultrasonic remote I knew of was a pneumatic Space Command. It emitted brief ultrasonic whistles when one of two buttons were pushed, which built up air pressure in an internal bellows then released it into a tiny whistle tube. This later gave way to a less bulky system that struck tuned metal rods with hammers.

[freebird5850]

That ultrasonic remote was fun to play with. We would jingle our keys in front of the TV and the channel would change.

I could make the Grandparents' tv channel change by raking my thumbnail down a plastic comb. Got my butt spanked too.