What is a Lucid Dream Induction Device?
Lucid Dream Induction Devices (LDID's) are equipment - usually electronic - which aid in achieving recognition that you are in a dream.
The Lucidity Institute developed a series of masks which employed infrared motion sensors to detect eye movement (REM) and LED lights which flashed as a signal to the wearer that they were in a dream. These masks culminated in the NovaDreamer (and the eventually-to-arrive ND 2), a somewhat comfortable battery-powered device with a decent range of customizability. I own this device, and as far as LDID's go, it's the best out there. It's also not been available for years now, and it isn't perfect (can lead to lots of awakenings and isn't quite comfortable enough).
The NovaDreamer is patent-pending, and a little complicated to build, so knock-off products which are available today are not as sophisticated. One such mask, the Remee, contains a flexible circuit board and has the basic flashing-LED system, and isn't the worst idea for use if combined with the Wake-Back-To-Bed method. We await an improved NovaDreamer, or something like it.
Other LDID's include smart-phone apps, reminder watches, audio-pillows, anything which can either train you to become more critical in dreams or signal to you while in a dream. Some smart-phone apps work by detecting your pattern of sleep motion in bed, and calculating the best time to either vibrate or send you audio signals by predicting when you are likely REM. I don't think these work so great. Reminder watches scroll messages on their screen at random or set intervals throughout the day (or night) and can help as training devices. I've had four of these, and they all malfunctioned. Audio-pillows can play a recorded audio loop, such as "check to see if you are dreaming!" The trick with any LDID is that their is no guarantee that sound or light will enter your conscious perception, or if it does, that it won't wake you up rather than trigger lucidity. AND, if the trigger does enter conscious perception, you still have to recognize the trigger for what it is and not confabulate its meaning into part of your dream story.
Something like the NovaDreamer certainly can work, and in fact worked for me the very first time I tried it. But it helps to be in a good mind-set for lucid induction for any LDID to play its role. Some of the success of an LDID may simply come from disrupting sleep. It is well known that breaking up sleep can instigate more vivid dreaming, and thus foster a more fertile ground for lucidity.