![]() ![]() I found by accident this worked to 10 yds in a lab when tuning a dipole back in the 70’s and later found commercial solutions doing the same. This is the same as using RSSI on a Return Loss bridge. VHF or UHF signals in a quiet channel using a splitter on one of the 2 ports can measure reflected signals off walls and detect reflections up to 10 or more wavelengths by using a Schottky diode and amp to detect changes in level using a constant power amp of ~100mW or so. There are probably many more, and depending on you exact use case, some or many may or may not be applicable. vibration sensors (MEMS or piezoelectric).distance sensors (ToF, ultrasonic, LIDAR…) and measure change.There are many, many other ways of detecting presence or motion, though, like PIR sensors, each has its own pros and cons, and many may not be suitable depending on what exactly you want to detect. You can't control the exact area they cover.They only detect heat sources, usually humans or animals. ![]() They only detect what they can see, so any obstacles will prevent them from seeing anything.Most only detect movement along a single axis (depends whether they use 2 or 4 surfaces and the shape of the Fresnel lens).They only detect movement in the plane orthogonal to the axis (it's a bit more complex than that, but it's a good approximation).They're usually not very sensitive at distances of a few meters.Given how a PIR detector works this seems highly unlikely. I’d be curious to see a PIR sensor that can actually detect fingers moving on a keyboard at any decent distance (1 or 2 meters), though. they don't see through walls or glass (useful to avoid detection of stuff "outside").they have no privacy or security issues (unlike camera-based systems for instance).they are solid state (no moving parts) and have very good reliability.they can have a pretty wide field of view.they don’t transmit anything (again, because they’re passive), which means they’re easier to get certified.they use very little power (since they’re passive) – very important for battery powered/wireless sensors.Question #3: Why do some PIRs in alarm systems have three LED lights yellow | red | green under the plastic sensor? I ask as perhaps they detect three different types of movement, so this might be related to the question and not off-topic. Question #2: Aside from microwave motion detectors potentially being problematic when they can detect movement through solid objects such as wooden walls, furniture, and glass which could lead to false alarms - why are they not used more frequently? I assume we should exclude sonar sensors since they are easily bypassed with a thin layer of fabric, such as wearing a bed sheet like a ghost, according to Myth Busters. It would be much more difficult to bypass if they detected movement. I ask this question because the above sensors can be blinded by a small glass picture frame placed over them, with a long pole. Question #1: Are there motion detectors which just detect motion, without the moving object having to radiate heat? I also understand there are some which are so sensitive they can even detect the body heat from fingers typing on a keyboard! This is described in detail in the supplied instruction manual and will only take you about 2 minutes.I grew up incorrectly believing that motion detectors (as part of burglar alarm systems) were designed to detect movement, when in actual fact it is the movement of a heated (like body heat) object which causes them to trip. Once you situated the motion detector, connect it to the ELRO AP5500 Alarm System wirelessly. Use the supplied mounting material to screw the motion detector against the wall at the location of your choice. Because the accessory is battery operated and communicates with the alarm system wirelessly, there is no need to deal with wires. Installing the AP55PR Motion Detector is very simple. Motion detector for the ELRO AP5500 Pro Alarm system.It also has an anti-tampering feature that sounds the alarm system when someone tries to remove or destroy the motion detector. The motion detector has a detection angle of 90° and detects at a distance of up to 12m away. When the AP55PR detects movement and your alarm system is switched on, your alarm will sound and you may be called by the system with an alarm message. With this motion detector you can protect an entire room against potential burglars. The AP55PR Motion Detector is an additional accessory for the ELRO AP5500 Pro Alarm System. ![]()
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