The clock, called SleepSmart, measures your sleep cycle, and waits for you to be in your lightest phase of sleep before rousing you. Its makers say that should ensure you wake up feeling refreshed every morning.
As you sleep you pass through a sequence of sleep states - light sleep, deep sleep and REM sleep - that repeats approximately every 90 minutes. The point in that cycle at which you wake can affect how you feel later, and may even have a greater impact than how long or little you have slept. Being roused during a light phase means you are more likely to wake up perky.
SleepSmart records the distinct pattern of brain waves produced during each phase of sleep, via a headband equipped with electrodes and a microprocessor. This measures electrical activity of the wearer's brain, in much the same way as EEG machines used for medical and research purposes, and communicates wirelessly with a clock unit near the bed. You program the clock with the latest time at which you want to be wakened, and it then duly wakes you during the last light sleep phase before that.
There's also a wristwatch version.