Yeah, this is doable, and I have done it in the past. You need an audio shield though. THen just put the recording as an mp3 on the SD card and trigger the playback when your sensor is activated.
ps (to the mods) the noobi handicap is really annoying for someone trying to be helpful. 5 min between posts completely kills forum functionality as a communication tool. Why would I help someone if it applies a time limit to when I can respond to someone helping me?