Strictly speaking, a Theremin uses a pair of antennae that act as capacitors in a specific R/C circuit. Looking at ...

Instead, it relies on an ultrasonic distance sensor to detect a hand (or foot) waved in front of the door. An Arduino Leonardo runs the show, sounding a buzzer when the ultrasonic sensor is triggered.

For the physical feedback, Denver has made some vibrating boxes that you put in your pockets. An Arduino polls the ultrasonic sensors and provides feedback via the boxes. This completely frees up the ...

A new ultrasonic fingerprint sensor measures 3-D image of your finger's surface and the tissue beneath it -- enhancing biometrics and information security for smartphones and other devices ...