Abstract: Apparatus for influencing a person preferentially to sleep on his side and not on his back. A gravity actuated sensor apparatus is attached to a sleeping person for detecting body position and to sound an alarm informing the person when he is resting on his back; thereby enticing the person to sleep on one side or the other and not on his back. Appropriate circuitry connects the sensor apparatus and alarm so that the alarm is actuated in response to the sensor apparatus detecting an undesirable body position. The sensor apparatus is positioned on one's head, or alternatively, is positioned on one's body. The alarm can be sensed by a sleeper to thereby induce the sleeper to move to an alternate position whenever he attempts to rest on his back for more than a few seconds.