A PIR (passive infrared) sensor reads the heat given off by a person or car moving across its field of view. PIR and infrared are the same technology, so there is no separate infrared type to choose between: the real choice is PIR or microwave. PIR needs clear line of sight, and it detects movement crossing the beam better than movement walking straight at it, so aim the head across the approach path. A microwave sensor instead sends out a low power radio signal and measures how the reflection changes. Because that signal passes through plasterboard, glass and thin plastic, a microwave sensor can be hidden inside a fitting or behind a diffuser, which is why sensor modules for LED battens are usually microwave. Microwave also picks up smaller movement. PIR is the usual pick outdoors because it is less likely than microwave to trigger on rain or on movement through a nearby wall. It is not immune to false triggers, so keep the head aimed away from sun warmed foliage, reflective surfaces and heat vents. Microwave suits stairwells, garages and storerooms, and it needs the sensitivity wound back if it starts detecting people in the next room.

For anything hard wired, yes. In Australia, connecting a mains powered sensor into a lighting circuit is licensed electrical work and must be carried out by a licensed electrician. Doing it yourself can void both the product warranty and your home insurance. The exceptions are the smart WiFi sensors, which mount to a surface and pair with an app rather than switching mains power, so check the individual product page for the power source. Plug and play modules made to clip into a compatible fitting are also simple to fit. Swapping an existing hard wired sensor for a like for like replacement is usually a short job for an electrician, since the wiring is already in place.

A photocell, also sold as a dusk to dawn or daylight sensor, ignores movement and switches on ambient light level instead. It turns the light on when natural light drops below a set threshold at dusk and off again at dawn, so the light runs all night without a timer you have to reset as the seasons change. It suits driveway and entry lights you want on continuously, signage, and any circuit you would otherwise forget to switch. Mount it where it can see the sky but where the light it controls cannot shine back into it, because that makes the sensor switch off, then on, in a loop. Some sensors combine both functions, using daylight sensing to stay inactive during the day and motion detection to trigger at night.

Range depends on the model and on the mounting height quoted in its specification. In this range, compact PIR sensors cover about 1.5 metres for a doorway or cupboard, exterior wall sensors are typically around 12 metres across a 180° arc, and 360° ceiling occupancy sensors cover an area up to about 24 metres across. Most wall mounted PIR sensors are designed to sit roughly 1.8 to 2.5 metres above the ground, and ceiling sensors are rated to a specific ceiling height, commonly around 2.4 to 3.5 metres. Mounting higher than the rated height widens the coverage area but reduces sensitivity, and mounting too low causes false triggers from pets and from anything moving close to the sensor, such as plants in a breeze. Always check the individual product specification, because the quoted range assumes the correct mounting height.

Usually yes. A stand-alone sensor wires in ahead of the light and switches power to it, so most standard fittings can be made automatic without replacing them. Three things decide which sensor suits. First, load: check the sensor's maximum rating covers the total wattage of everything it switches, which in this range runs from about 500W up to 1000W or a 16A rating, and check the sensor states LED compatibility, because some sensors have a minimum load or pass a small current when off, which can make a low wattage LED glow faintly or flicker. Second, location: IP44 or higher is the minimum for a covered porch or eave, and in practice that means the IP65 and IP66 units on this page, which also handle a fully exposed wall. Third, mounting: pick recessed, gimble recessed, surface mounted or wall mounted to match the surface you have. There are also retrofit and plug and play modules made to fit inside existing fittings such as LED battens. A licensed electrician should do the wiring.

Most sensors have three small adjustment dials under a cover on the body. LUX sets how dark it has to be before the sensor will trigger at all: a sun symbol means it will also work in daylight, a moon symbol means night only. TIME sets how long the light stays on after the last movement it detected, typically about 10 seconds at minimum up to around 15 minutes at maximum depending on the model. SENS, sometimes marked RANGE, sets how far away and how readily the sensor picks up movement. A good starting point is LUX on the moon symbol, TIME low, and SENS around halfway, then walk test after dark and adjust one dial at a time. If a light will not switch off, the usual causes are the LUX dial set for daylight, the TIME dial at maximum, or the sensor left in manual override. To clear manual override, switch off at the wall and leave it off for at least 60 seconds so the sensor discharges, then switch back on. If that does not work, switch the lighting circuit off at the switchboard for a minute.