Low cost personal biofeedback devices. Designed to detect REM sleep.

Frequency Monitor – $128
A headband with an accelerometer that is sensitive enough to pick up the heartbeat and can thus easily detect rapid eye movements.
Resolution: 3660µg, measurement range: ±5g (49 m/s2)
LSDBase Entries | DIY | Pre Order

Electroencephalograph – $256
A headband with an electroencephalograph based on the OpenEEG project. Detects REM sleep from the spikes in electrical activity caused by the eye muscles, but also records the unfiltered brainwaves.
Active electrodes: 4, passive electrodes: 1
LSDBase Entries | DIY (EEG SMT, 4 x AE, 1 x PE, 1 x USB) | Pre Order

To make one professionally, suit up and get two halo headbands (one white tie, one black pullover and some iron on tape so you can make a smugglers belt in the middle for the cables and sensors).

Halovision – $64
A headband with a spy camera that is sensitive enough to see the movements of the eyes behind closed lids. Pro tip: draw a contrasting triangle on your eyelid.
Range: 150m
LSDBase Entries | DIY | Pre Order