When it comes to selecting internal alarm sensors, what are the features installers should be looking for? Are all internal sensors the same or do some offer superior catch performance and false alarm resistance?

WHAT makes for a quality internal alarm sensor? That depends on the environment the sensor is installed in – the more challenging the environment, the better the design and quality need to be. In many internal applications, passive infrared sensors are the perfect solution, while for more challenging internal environments, you need to look at dual technology detectors. 

When selecting a PIR for internal use look for dual or quad multiple pyro-electric sensing. These reduce false alarms through increased stability. Other features you should rate highly include creep zones, a good-sized detection window, not just a slot or a small hole; and RFI, surge and low-voltage protection. You also want zone adjustment that allows range to be changed or particular zones to be ignored, latching (with LED indicator), walk test capability (and LED indicator). 

You want a high signal-to-noise ratio, anti-masking, tantallum capacitor circuits for EMI/RFI rejection, trouble log, silent alarm relay, enhanced processing, temperature gain compensation and a tamper switch. Other beneficial features include site adjustable sensitivity, first-to-alarm memory, low voltage signal and auto self test. 

The best PIRs will have dual edge or quad sensing zones and an array that offers a significant number of look down zones, as well as more than one sensing range and the greatest possible number of discrete zones. They’ll have surge and low voltage protection, adjustments letting you alter the range of mask zones, as well as LED-supported latching. A plug-in test meter is an advantage. 

Once the temperature gets over 35C, any PIR is going to be seriously disadvantaged even if temperature compensation is fattening up that tiny pyro signal through an amplification circuit. If things are going to be warm or there will be direct sun on glass, you should think quality dual technology. Dual technology sensors combine a pair of technologies that are sensitive to 2 different types of disturbance – microwave and PIR. 
The thinking behind this is to ensure that each sensor supports the weaknesses of the other to eliminate false alarms. 

It works thanks to the intrinsic nature of each of these 2 sensing technologies. PIR elements sense the level of IRE changing between zones over a set time at a set speed. There aren't many environmental disturbances that mirror this sort of activity – but heat sources, especially warm air currents, spell trouble for PIRs. 

Microwaves work differently. They cover an area with a signal and then pick up variations between the signal sent and the signal reflected back. It's called the Doppler shift. Microwave sensor technologies offer strong detection performance – they'll pretty much detect anything that moves. In terms of dual technology, what's vital is that PIRs are sensitive to movement across their zones, while microwave devices activate if they pick up a Doppler shift that moves either towards the sensor or away from it. 

Paradox DG75

Who has what?

According to iTech, the company’s best internal sensor is the hard-wired Crow Swan Quad PIR with 18m standard wide angle lens. The unit’s specifications include quad element PIR (pyro-electric) sensor, bi-directional temperature compensation for consistent catch performance when hot and humid, pet immunity to 25Kg (adjustable), 18m wide angle detection distance with range adjustment and tamper protection. Setting it apart from the competition are reliability and consistent performance within wide environmental conditions.

According to iTech, “Although most installers perform this task successfully, it’s important that the appropriate sensor technology (PIR or dual technology) is selected for a given application. The one-type-fits-all installation undertaken because the end user may want all sensors to look the same, or because of under quoting to win the installation, can result in poor overall system performance that may require site re-visits. 

“Equally as important as appropriate selection of sensor technology, is the correct sensitivity adjustment and walk testing of a sensor onsite,” iTech says. “If sensors are left at their factory settings, they are more likely to false alarm due to over sensitivity that is inappropriate for the size of room they are installed in or because of environmental conditions in the installed environment.”

Over at Bosch Security Systems, the leading internal sensor is the Blue Line Gen2 TriTech range, which has dynamic temperature compensation for superior catch performance and microwave noise adaptive processing to reduce false alarms from repetitive sources.

The Blue Line Gen2 has wall-to-wall coverage when installed in applicable environments giving superior catch performance. Other features include flexible mounting height and no installer adjustments, so as to reduce installation time and false alarms, improve catch performance. The sensor has a self-locking enclosure with integrated bubble level to assist with fast installation, There’s a pet friendly selectable model available for pets up to 45kg.

Bosch Blue Line

According to Paul Knight at CSD, the company’s leading internal intrusion sensor for domestic and small commercial applications is the Paradox DG75 with high-security digital motion detector with pet immunity. Core specifications include dual optics (2 dual opposed PIR element sensors), pet immunity using a patented combination of advanced optics and digital processing technologies to be immune to pets weighing up to 40kg, digital dual opposed detection and an 11m x 11m, 90-degree viewing angle. There are both wired and wireless options available. 

“What sets the DG75 apart from the competition is the fact it is extremely reliable and false-alarm free. Reliability, ease of installation and value for money are the key things installers need to be looking for.”

Swan Quad from iTech

Meanwhile, Honeywell has a huge internal intrusion sensor range including the IS2500 Series, 5800 Series Wireless, DT7200 Dual Tec Series, DT7400 Dual Tec Series, DT900 Dual Tec Series, and the Ceiling Mount Series.
For instance, the IS2500 PIR is hard wired, has a mounting height of 2.3m to 2.7m, uniform sensitivity optics, patented mirror look-down (creep) zone, dual-slope temperature compensation, microprocessor control, silent tamper proof relay, 45-degree terminal blocks, DIP-switch programming, spare EOL terminals, automatic walk test mode and 4 sensitivity settings.

Honeywell IS2535T

Models in the range include the IS2535T (3-in-1 PIR) with 11m x 12m range and (selectable 0, 18, 36kg pet immunity); and the IS2560 PIR with 18m x 26m range and the IS2500 PIR with 30m x 6m range.

When it comes to dual technology sensors, Honeywell’s offering includes the DT7200 Series which features K-Band technology for better pattern containment and shaping, resulting in superior false alarm immunity, a sturdy, attractive housing, uniform sensitivity optics and temperature compensation. There’s zero clearance black bug guard, mirror look down and microwave supervision. Models available include the DT7235 11m x 11m Dual Tec with 45kg pet immunity and the DT7235TCE with 11m x 11m Dual Tec without pet immunity. 

According to Honeywell, the company’s range of PIRs and dual technology sensors is “rigorously challenged in state-of-the-art test rooms built to exceed the toughest SIA standards. This means an installer should never have to compromise between performance and false alarm prevention when selecting an intrusion sensor.”

Paradox DG75 coverage