The Nap Zapper is a simple device that could just save your life- or help you keep your job! The small, flexible device rests comfortably over the top of your ear and will sound an alarm to wake you if you start to doze and your head nods. The Nap Zapper is lightweight and comfortable to wear (approximately the size of an external hearing aid) and is fully adjustable. Perfect for sleepy drivers or someone working the late shift and having trouble staying awake. It works great for security guards, machine operators, and even students struggling to stay awake while studying. The unit requires 3 LR41 batteries that are included. It measures two and three-quarter inches x two inches x one-half inch.