IF you’re putting in heat detectors when building a security system, don’t just go for the cheapest ones you find, think about the application to avoid false alarms, especially in commercial or industrial applications.

All heat sensors incorporate bimetallic switches that stay open under a temperature of 57.7C but they’ll close once the temperature gets higher. When the switch closes, a circuit is completed, and an alarm is activated – simple enough.

But these heat sensors are going to be vulnerable to legitimately high temperatures in locations like metal sheds, and industrial or manufacturing sites. The upper spaces of steel and glass buildings will also give trouble.

If there’s a likelihood of higher than normal temperatures, then think about using higher temperature heat sensors. You can buy units that won’t activate until the temperature passes 93.3C). While you wouldn’t think so, a fire raises temperature at the highest point in a room or building very fast – much higher than 93.3C within minutes of actual flame. If you’re in any doubt, however, go for sensors that activate at lower temps.

When installing commercial and especially domestic systems, be aware that dangerous levels of smoke can be produced without a significant increase in temperature. Never install heat sensors alone in a domestic environment. Go for photoelectric smokies and use more than you need – at least one on each level depending on the size of the home.