i've got the fisher price sound and lights monitor (i think that's what it's called). it lights up with noise (has five lights that light up according to how loud the noise is - kind of like a noise-meter IYKWIM). it was about $50-$60 from memory. the receiver can be battery powered too. i got it from k-mart when bub was first born and it's still going strong.
I googled it and yes the FP is the one we have - and the lights are on the remote unit, has one big light on base unit. It is very good - I'd go for that one. I think it cost about $60.