College design project

I got an interaction design project for my MFA and i would like to build a fairly simple circuit for it: a sensor with two parts - when they are aligned a relay or a switch of some sort goes to high and triggers sound playback. I have a bunch of questions, mostly about what parts i should use: what should i use for the sensor, for the brain and where should play the sound from - would a CD walkman work or can i get a raw sound storage and playback circuit, the kind they use inside some teddy bears?
Any and all ideas are welcome and appreciated.
Thanks in advance.

This might interest you for the sound playback: Official homepage of TalkBotBrain.com