Which of the following is NOT one of the three types of alarm systems?

The correct choice identifies "Visual Alert" as not being one of the conventional types of alarm systems typically categorized in security contexts. Alarm systems are generally designed to notify personnel of potential threats or emergencies through sound or silent signals. The three main types include:

1. Silent Alarm: This type of alarm is used to alert security personnel discreetly without alarming the intruder or suspect. It’s common in situations where a quiet response is needed to avoid escalating a threat.

2. Audible Alarm: This system emits a sound, such as a siren or bell, to alert individuals in the vicinity as well as deter potential intruders. The loud noise is meant to draw attention and prompt immediate response from security or law enforcement.

3. Combination Alarm: This incorporates features from both the silent and audible alarms, providing flexibility in response strategies. It can offer alerts both with and without sound, depending on the situation’s requirements.

"Visual Alert," while it can be a notification method in other contexts (like in emergency systems or notifications), does not fit within the primary classification of alarm systems in basic security terminology, which focuses on audio and silent response systems.