Burglar (or intrusion), fire and safety alarms are all electronic today. Sensors are connected to a control unit via a low-voltage hardwire or narrowband RF signal which is used to interact with a response device. The most common security sensors indicate the opening of a door or window or detect motion via passive infrared (PIR). New construction systems are predominately hardwired for economy. Retrofit installations often use wireless systems for a more economical and quicker install. Some systems serve a single purpose of burglary or fire protection. Combination systems provide both fire and intrusion protection. Sophistication ranges from small, self-contained noisemakers, to complicated, multi-zoned systems with color-coded computer monitor outputs. Many of these concepts also apply to portable alarms for protecting cars, trucks or other vehicles and their contents (i.e., "car alarms"). See also fire alarm control panel for specific fire system issues. Burglar alarms are sometimes referred to as alarm systems, see burglar alarm control panel for a discussion of hard-wired burglar alarm system design.

Burglar alarms (or perimeter detection systems, Perimeter protection, intrusion detection systems and many more terms for the same thing) are divided to two main fields: home burglar alarms and industrial burglar and perimeter intrusion detection.

Home burglar alarms

Home burglar alarms are often systems assembled from inexpensive infrared detectors that the home owner or the security contractor will install in front of all the windows and doors in the house. These infrared sensors are designed for indoor use only and should not be used outside. The cost of installing outdoor sensors is higher and false alarm prone. A more complete home alarm also includes magnetic sensors on the doors and windows. These sensors will alarm the system when a door or window is opened. These sensors do not protect against glass breakage, but additional glass break detectors can also be used. The sensors are connected to a control panel that is operated by a keypad. The control panel processes intrusion signals and rings sirens and/or communicates to a monitoring service which then calls the owner and/or police department. This is the basic form of home alarm system.

Industrial perimeter intrusion detection systems

Indoor

'''These types of sensors are designed for indoor use. Outdoor use would not be advised due to false alarm vulnerability and weather durability. '''

Passive Infrared Detectors
The passive infrared detector (PIR) is one of the most common detectors found in household and small business environments because it offers affordable and reliable functionality. The term passive means the detector is able to function without the need to generate and radiate its own energy (unlike ultrasonic and microwave volumetric intrusion detectors that are “active” in operation). PIRs are able to distinguish if an infrared emitting object is present by first learning the ambient temperature of the monitored space and then detecting a change in the temperature caused by the presence of an object. Using the principle of differentiation, which is a check of presence or nonpresence, PIRs verify if an intruder or object is actually there. Creating individual zones of detection where each zone comprises one or more layers can achieve differentiation. Between the zones there are areas of no sensitivity (dead zones) that are used by the sensor for comparison.