What is a Sounder in an Alarm System?

Industrial fire alarm systems use sensors to detect changes in temperature, the presence of smoke or a combination of both. Thermistors are used to detect heat from a fire, while smoke can be detected using ionisation or photoelectric sensors.

A thermistor, or thermal resistor, is a semiconductor whose resistance varies based on temperature. Negative temperature coefficient (NTC) thermistors are commonly used in fire alarm systems as temperature sensors. Their resistance decreases with increased temperature and can be used to trigger an alarm.

Smoke detectors may use a radioactive isotope to ionise a small volume of air, allowing a current to be conducted across an air gap. The presence of smoke in the unit will absorb the alpha radiation, eliminating the movement of ions and triggering the alarm.

An alternative smoke detector uses a light source which is reflected onto a photoelectric sensor by the presence of smoke. These photoelectric smoke alarms are more useful for slow-burning, smouldering fires, while ionisation smoke alarms respond quickly to fast-burning, flaming fires.

When the fire sensor is triggered, the most important output is an audible alarm sounder so that the building can be evacuated as soon as possible. Other outputs may include visual outputs on a control panel to identify the location of the problem, along with automatic contacting of the emergency services. 

With a range of sensors, electronic sounders, beacons and signal towers, the RS automation signalling range has everything you need for alarm installations.

The alarm sounder is an essential part of a commercial system, alerting employees to the emergency. Sounders are usually wall-mounted and installed at key locations around the facility to ensure complete coverage. A range of electronic sounders is available, with a variety of sounds including sirens, klaxons, buzzers, horns and even voice recordings used to convey evacuation instructions.

Electronic sounders can also be ruggedised for industrial applications and loud enough to be heard in very noisy environments where production machinery is being used. Different sounds can also be used to indicate different types of incidents are taking place. 

Some electronic sounders are combined with lights to produce audio and visual alerts. To choose the correct sounder for your alarm installation, consider the needs of the specific building. Think through the required volume and number of positions which need a sounder. 

With a range of IP ratings, ATEX-approved options and durable construction, RS has a comprehensive range of electronic sounders. 

A range of alarm sensors is used depending on the purpose of the alarm.

For fire alarms:

• A thermistor-based sensor may detect temperature increases.
• An ionisation sensor may be used for smoke detection.
• A photoelectric sensor can be used for smoke detection.

For intruder alarms:

• Magnetic sensors detect the opening of doors and windows.
• Glass-break sensors include a microphone to detect the sound of breaking glass.
• Passive infrared (PIR) sensors detect motion.
• Vibration sensors detect forced entry.

The complexity of the control panel of a commercial alarm system will depend on the needs of the installation. At the most basic level, the control panel allows the commercial alarm system to be set and reset, usually by entering a numerical code. More advanced control panels allow separate zones of a factory or commercial premises to be controlled separately. They may display information about where the alarm has been triggered.