Low cost personal biofeedback devices. Designed to detect eye movements during sleep.
Halovision (EOG)
A night-vision (infrared) camera that detects rapid-eye-movement patterns behind closed eyelids in the dark. Like having your own personal sleep lab technician watch you sleep and alert you when you are dreaming.
Order Now | LSDBase Entries | Lucid Scribe Plugin | Firmware: Full, Update

Halovision INSPEC – €256:

Research edition – €140:

Smart-mirror edition (obsolete):
Coder's Halovision

Electroencephalograph (EEG) – €192 (obsolete)
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 | Lucid Scribe Plugin | DIY (EEG SMT, 4 x AE, 1 x PE, 1 x USB)

Frequency Monitor (FM) – €128 (obsolete)
A headband with an accelerometer that is sensitive enough to pick up the heartbeat while resting.
Resolution: 3660µg, measurement range: ±5g (49 m/s2)
LSDBase Entries | Lucid Scribe Plugin | DIY

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).