This device will keep you awake and will always protect you from unintentionally falling asleep when you're behind the wheel or lurking when to spying someone. It works on the principle of balance. When you accidentally fall asleep the head goes forward or sideways. When this happens, an acoustical signal will immediately wake you up.
Put the device behind the ear and by moving it around the ear select the desired position. Thus you can test what position of the head will trigger the audible alarm. When you set the preferred position you can make sure that you will not fall asleep and miss the spied subject.