[John Boxall] took a different route for a single-input combination lock. This unit uses a Ping ultrasonic range finder to input a four digit code. It’s a hardware upgrade, but uses the same basic ...

Infrared certainly has its uses, but if you’re trying to locate objects, ultrasonic detection is far superior. It’s contact-less, undetectable to the human ear, and it isn’t affected by smoke, dust, ...