Although the basics of the alarms are the same -- a sensor in the underwear or pajamas detects moisture and triggers an alarm -- there are some slight differences among models.
In most models, a wire runs from the sensor to an audible alarm, which is attached with Velcro to the shoulder of the child's pajamas. The alarm is loud enough to awaken the child and a parent, who can lead to the child to the bathroom and make sure he changes his underwear before going back to sleep.
Adolescents, however, may prefer a wireless bed-wetting alarm that vibrates when it senses moisture. Because it is wireless and silent, only the wearer is aware when the alarm goes off.