I'm looking for some small sensors (less than a cm) which can detect the distance between each other within a range of about a meter or so. I've been looking at "proximity," "distance," and other noun, and all I can find are the kinds of sensors which detect proximity to a wall, or light source, when what I need is something that will only detect the other sensors, likely via radio.

Does anyone know of an existing package like that, or is this something I would need to DIY?

EDIT: To be clear, these sensors would not be mounted on a fixed axis, so line of sight wouldn't work. Also, I would like to use more than three, so since since they need to be able to communicate on different bands I might have just answered my own question.

how abouth infrared LED and reciever. SMD reciever can be really small and will only work on 38KHz.