As with most great stories, the story behind the foot traffic monitor begins with a bet. You see, this semester I have no morning classes on Monday's, Wednesday's, or Friday's. Often times, I would sleep in on these days, only to be woken up by my friends' walking into my room unannounced. I told them they always woke me even though I pretended to be asleep, and they insisted there were various times they had successfully snuck into my room uncaught. Naturally, a bet was formed and plans to monitor the opening of my door drawn up.
The result was the foot traffic monitor (which happened to have much more applications on top of winning bets!). It uses the hypersonic sensor to detect a change in distance caused by the opening of the door. To avoid double-counting, when a change in distance is detected, the device waits a designated period of time before taking the next measurement. The 4-digit display is used as a counter from 0-9999, recording how many times a door opens while the device is active.
The attached video shows how the device was used to monitor the standings of the bet, recording how often someone walks into my room. However, the foot traffic device also has practical uses in business: foot traffic in a retail store, security: can be paired with a buzzer rather than 4-digit display for use as alarm, and road traffic control: monitor roads near potential construction with high traffic.