Alarm kits with siren

 

— the presence of its own siren in the standard configuration of the set.

The siren provides an audible and, in some models, a light alarm; sometimes this is enough to stop an encroachment on a protected object or to attract the attention of security / law enforcement officers. Such equipment can also be purchased separately (if the control panel has an appropriate output, see "Control panel options"). However, in most cases it is more convenient to buy a system that was originally equipped with a siren: this will allow you not to worry about compatibility, and complete sirens usually give out more than a decent number of decibels.