There are various types of motion detectors, and not all of them are as effective as others at securing your home. Different types have been designed for different purposes, and although all of them will be effective, some will be more likely to produce false positives, which is a problem for alarm systems.

One of the most popular types of motion detectors are infra-red light sensors. Infra-red is a light which is invisible to human eyes, so it should catch people off guard, so long as they don’t have any infra-red sensing equipment themselves. They work by streaming a line of infra-red light between two points, creating a feedback loop. If anything enters the space between the two points, then the loop is broken, and the alarm is then triggered. This is hardly a fool-proof system, but it is unlikely to be alerted by anything you don’t want to be alerted by.

Alternatively you have sensors which monitor their immediate acoustic fields for any changes. These can produce false-positives with greater frequency, but provided the circumstances are well matched to their function then you will have something which works amazingly well.