Alarm sensors that can pass through walls.

[glf]

As a title, what are the technologies of alarm sensors that can detect movement through walls?

From what I know are only those who use microwave technology up to 10 Ghz.

Any indication in this regard is welcome.

[sixwheeledbeast]

Some microwaves will pass through walls but the sensors are not designed to "detect" through the wall.

Is this a theoretical question or can you explain what you are trying to do/work out?

[glf]

Simple curiosity: I knew that microwaves up to a certain frequency (10ghz?) could cross walls and generate false alarms.

I wanted to know whether other types of sensors, such as ultrasonic detectors or other technology, could also be affected.

[PeterJames]

Microwave are the only detectors available that will see through solid objects, they use radar dopler which travels through solid objects and detects changes, such as moving objects. Whereas ultrasonic use sound a bit like how a Bat hears, there is a tx and an rx they tx a ultrasonic noise which bounces around the room and at the same time the rx listens to that noise. If anything in the room moves the sound it receives changes. Infra red see's heat movement.

[sixwheeledbeast]

Microwaves will both penetrate and reflect back from surfaces, the reflected signals are processed to detect changes. Ultrasound will penetrate thin surfaces (for example a sonograph) but most if not all would be absorbed or reflected by surfaces when used in a detector.Ultrasonic went out of favour and replaced with other technologies like IR and MW due to health concerns.

Any detection method that could penetrate outside of the protected area would normally be in a combination detector now (a DT or Dual-Tech), the other technology being passive infrared as the idea is to detect movement only within the area you are protecting. Installers would adjust and test the MW range on detectors they fit to avoid false alarms.

[al-yeti]

Thermal imaging would do it 

[glf]

18 hours ago, al-yeti said:

Thermal imaging would do it 

 

I have a Flir E6 - EX and unfortunately thermal cameras can't see through walls. TI can see differences in the temperatures in buildings and structures. So you can see wall studs, window frames, a/c ducts, etc. These cameras only “see” heat as it radiates off of an object. It may “see” the heat coming from a house, but it can’t see into the house because the camera picks up the house’s exterior thermal image first. In fact, the thermal imaging doesn’t even see through glass because the glass has its own thermal profile.

[glf]

Is it physically possible that the microwaves crossing the wall generate a false alarm for only half of the room crossed, not causing problems in the other half ?

[PeterJames]

10 hours ago, glf said:

Is it physically possible that the microwaves crossing the wall generate a false alarm for only half of the room crossed, not causing problems in the other half ?

Can you say that in English?

[al-yeti]

44 minutes ago, PeterJames said:

Can you say that in English?

You you Brexit person