Proof of concept to use a single Puck to detect people passing a corridor with IR emit/receive

It might work - you could definitely give it a try. However you may fall foul of Puck.js's relatively limited IR transmission range (which is only maybe 1M - depending on how good the receiver is).

Another option might be to use a red laser (and lasers are obviously cooler anyway) and then point the reflection back at the Puck's red LED (which is what is used for measuring light).

Or... you could cheat and use something like: http://www.espruino.com/Pyroelectric

They'd need another source of power but they are pretty efficient so would run for a while on a battery.