You would have eyes on the back of your head. Or inside your house. Or anything. It would be wonderful if you could see immediately if there was anything suspicious going on in your home, even if you are not there. This would allow you to determine if there was a burglary.

What are you supposed to do? You can install futuristic mechanical eyes in your home with the help of locksmith Liverpool Street.

Well, yes. Motion sensors are able to detect if something is moving in your home and send an alarm signalling the police or burglars. Are they worth the effort? What is the working principle of motion sensors?

This is everything you need about motion sensors.

1. PIR Sensors

2. Microwave Sensors

3. Ultrasonic Sensors

How Do Motion Sensors Work?

Motion sensors are smart devices that can “see” what is in front of them, often without the need for a camera. They can be used to monitor your home continuously. How do motion sensors work?

PIR Sensors

The most popular type of motion sensor is the passive infrared (or PIR) sensor. They are more practical because they use less energy than other types.

How PIR Sensors works?

They are called passive security sensors, as they don’t emit any sound waves or microwaves. They can instead “read” infrared signals from their surroundings to detect movement.

Everything emits infrared radiation. It is impossible to make something not emit infrared radiation if you remove all heat and turn it to absolute zero temperature. This is something scientists are currently unable to do, and would also kill burglars.

Microwave Sensors

The original ultrasonic sensors are based on the same principles, but microwave sensors work more efficiently. They can see through walls but are not always as effective if there is a lot of activity in a monitored area.

How Microwave Sensors Work

To work, they use a type of radar. These devices project microwaves onto surfaces and then measure the microwaves’ return to the sensor. If there is a change in the way these microwaves return to the sensor, there will be motion.

The Doppler Effect is used to calculate the sensor’s precise motion. Do you know how car engines sound higher when they are far away, but then suddenly become lower-pitched as they move closer to you?

This is the Doppler Effect. Car movement causes sound waves to become closer together, making them higher.

Take sound waves and apply the same principle to microwaves. Sensors can determine how microwaves were moved before they reflect back to them.

Ultrasonic Sensors

Ultrasonic sensors were the first type of motion sensor, but they have been outpaced by other technology. However, they are still useful for certain applications.

How Ultrasonic Sensors work

Ultrasonic sensors operate by echolocation. You don’t have to bother anyone by activating them. They emit sounds that are far too loud for people to hear. The sound waves are then measured to determine how they bounce around the environment.

If the sound wave pattern changes, it means that there was a movement. The alarm sounds when the sensor has been armed.


Motion detection technology allows you to see your house from a distance. It can be used to detect if someone has broken into your home while you are away.

They are not perfect by themselves. Each type of motion detector has its pros and cons. A good lock is required in order to ensure safety.

Combining these perimeter security measures by locksmith Liverpool Street can stop burglars from getting into your house and protect your belongings for when you have to leave.

Reach out to us at EC1 Locksmiths today and our Locksmith Liverpool Street team will be with you in no more than 15 minutes to figure out all of your needs.