Alarms that detect dream state

Hi
my friend has one of these alarms that detect when you are in shallow sleep/dreaming from your amount of body movement

Advanced MP3 Players aXbo Couple Sleep Phase Alarm Clock

The idea is it wakes you up then as its easier to awake from a shallow sleep state.

But...couldnt this be used to play a sound you set as a dream sign when it detects you are dreaming? At a level that doesnt wake you up but penetrates your dream?

I have been experimenting with using music as a link between real and dream worlds...it works! I went to see Inception yesterday, and they used the same technique : to play a chosen song as a sign for you to recognise in yr dream. So far, I have recognised the song I've set (using an iphone alarm clock that can play plylists of songs as an alarm), but have not recognised it as a dream sign. Quite frustrating but I'm hanging in there.

What I want is a device like this alarm clock but that lets you choose music instead of alarm noises. Does anyone know if such a device exists?

thanks
Matt