A capacitive sensing system senses the presence of an object proximate to an antenna using a sensing field signal having a sensing field frequency. The capacitive sensing system can be used in security systems, to provide an alarm if a valuable object is removed from where it can be detected. The capacitive sensing system can also be used to provide an alarm when an object is detected near a moving member, such as a parking barrier gate, sliding gate, elevator door, garage door, or window. The sensitivity of the system may be adjustable according to one or more conditions, such as position of the moving member, time of day, or operator inputs (for example, to put the system into a maintenance mode having low sensitivity). Systems may also have a cut-out, in which alarms are suppressed.