Over at tronixstuff the team has created some ... different projects, and one of these is their Ultrasonic Combination Switch. As an Arduino can generate a number relative to the distance measured by an ultrasonic sensor, this switch is activated by the user placing their hand at four different and fixed distances away from the sensor over a period of time. If the user manages to match the predetermined distances, the switch is activated. For example:
Apart from amusing or irritating those around you, this project offers a futuristic alternative to using a keypad or keyswitch for electronic locking purposes. For more information, Arduino sketches and directions visit the project page. To move forward with Arduino-embedded projects, consider the Freetronics LeoStick - one of the smallest Arduino-compatibles on the market with onboard USB, RGB LED and piezo:
