Loughborough University Sleep Research Centre researchers found that delta waves (in the range of one to four Hz) remained dampened for nearly one hour after a nearby cell phone was shut off. These brainwaves are the most reliable and sensitive marker of stage two sleep.

Although the test subjects had been sleep-deprived the night before, they could not fall asleep for nearly one hour after the phone had been operating (without their knowledge).

In another study, Swinburne University of Technology researchers found that cell-phone radiation boosts alpha waves (eight to 12 Hz) in the brain.