The correct choice is the swinger alarm, which refers to an alarm system that activates either due to external stimuli or internal faults, leading to a repetitive cycle of false alarms or activations. This type of alarm typically has a threshold for activation, and if it experiences issues such as a loose connection or environmental disturbances, it can trigger multiple alerts in a short period.
In the context of the other options, fire alarms and CO detectors activate based on specific and serious conditions—such as the presence of smoke, fire, or carbon monoxide—making them less likely to trigger multiple false alarms due to malfunctioning. Door contact sensors, which indicate whether a door is opened or closed, are generally straightforward and do not have the multiple activation issues associated with swingers unless there is a significant wiring or installation fault. Thus, it's evident why the swinger alarm is specifically noted for its propensity to cause multiple activations when malfunctioning.