Reference Terms
from Wikipedia, the free encyclopedia
Passive infrared sensors
Passive InfraRed sensors (PIRs) are electronic devices which are used in some security alarm systems to detect motion of an infrared emitting source, usually a human body.
All objects, living or not, whose temperature is anything above absolute zero emit infrared radiation. This radiation (energy) is invisible to the human eye but can be detected by electronic devices designed for such a purpose. The term 'passive' in this instance means the PIR does not emit any energy of any type but merely sits 'passive' accepting infrared energy through the 'window' in its housing. An intruder entering the protected area is detected when the infrared energy emitted from the intruder's body is focused by a Fresnel lens or a mirror segment and overlaps a section on the chip which had previously been looking at some much cooler part of the protected area. That portion of the chip is now much warmer than when the intruder wasn't there. As the intruder moves, so does the hot spot on the surface of the chip. This moving hot spot causes the electronics connected to the chip to de-energize the relay, operating its contacts, thereby activating the detection input on the alarm control panel.
Related Stories
1
2
Matter & Energy News
August 8, 2026
Aug. 8, 2026 A new nanostructured carbon design lets fuel-cell catalysts use tiny amounts of platinum while remaining remarkably stable and efficient. The breakthrough could help hydrogen fuel cells become a more practical way to power data centers, vehicles, ...
Aug. 8, 2026 Scientists have created the first quantum material that can sort and transport different quantum states of light at room temperature, potentially removing the need for bulky, ultra-cold refrigeration ...
Aug. 7, 2026 Scientists have generated quantum entanglement directly from sunlight, potentially offering a lower-energy alternative to the lasers normally used in quantum technology. Their outdoor experiment produced entangled photons with about 94% similarity ...
Aug. 7, 2026 Scientists have demonstrated that heat can move through a crystal in focused, wave-like rays at room temperature instead of spreading randomly. The breakthrough could make it possible to route heat around sensitive parts of next-generation chips and ...
Aug. 6, 2026 A new hollow nanoreactor mimics living cells to make hydrogen peroxide more efficiently using visible light. Its light-trapping cavity and proton-shuttling shell could open new possibilities for cleaner chemical manufacturing and artificial ...
Aug. 4, 2026 Scientists have successfully generated electricity with a hydrogen turbine that produces its own pressure through detonation waves instead of relying on a mechanical compressor. The breakthrough could unlock dramatically more efficient power systems ...
Aug. 4, 2026 A new 3D printing technique can produce exceptionally hard tungsten carbide cobalt while using less of its expensive raw materials. By softening rather than fully melting the material, researchers created defect-free samples with industrial-grade ...
Aug. 3, 2026 Researchers have found a way to build much larger “twisted” oxide materials while precisely controlling how their atomic layers line up. Because these materials can be made over large areas and transferred onto different surfaces, the technique ...
Aug. 1, 2026 A surprisingly simple change could make sodium-ion batteries far more powerful while opening the door to turning seawater into drinking water. Researchers at the University of Surrey found that sodium vanadium oxide performs much better when its ...
July 31, 2026 A new chemical process can transform three of the most common plastics into high-purity hydrogen without sorting them first. The technique operates at much lower temperatures than traditional ...
July 31, 2026 Scientists have built the first all-optical photonic time crystal, allowing them to reshape the behavior of terahertz light at extraordinary speeds. The breakthrough could open the door to ultrafast computing, smarter communication systems, advanced ...
July 30, 2026 Engineers have transformed a notoriously brittle cobalt-aluminum compound into a material that is both extremely strong and capable of bending without breaking. Their nanoscale design produced a ...
Latest Headlines
updated 12:56 pm ET
Aug. 5, 2026 A massive magma reservoir has been detected deep beneath Tuscany, despite showing no obvious signs at the surface. Scientists mapped the roughly 6,000-cubic-kilometer body using natural ground ...
Aug. 3, 2026 When atomic nuclei smash together at nearly the speed of light, they create the hottest fluid in the universe, but scientists may have overlooked one of its most important forces. New simulations ...
Aug. 1, 2026 Scientists have identified LHAASO J1912+1014u as a cosmic accelerator that can push protons beyond one quadrillion electron volts. The finding may ...
July 31, 2026 Scientists traced a mysterious surge of low-energy gamma rays from zinc-70 to magnetic changes occurring inside its nucleus. The breakthrough could improve models of how stars, supernovae, and ...
July 30, 2026 Physicists have uncovered a surprising limit to electrical resistance caused by particles colliding. Using ultracold potassium atoms trapped in a grid of light, researchers created a highly ...
July 29, 2026 Ultrafast X-rays revealed how a molecule converts absorbed light into motion in just trillionths of a second. Individual atoms recorded different stages of the process, opening a powerful new window ...
July 29, 2026 Rice University chemists have found a new way to make neodymium, a rare-earth metal, interact with oxygen. Using a specially designed molecular structure described as a “basket,” the team ...
July 28, 2026 Scientists have created twisted laser beams that interact differently with right-handed and left-handed molecules, revealing their identity through the fragments they produce. The approach could ...
July 24, 2026 A new analysis suggests the Sun holds far more silver than earlier estimates indicated. More advanced models of the solar atmosphere raised the calculated amount by 55 percent, bringing it into much ...
July 22, 2026 Researchers discovered a proton-assisted mechanism that greatly improves how triplet energy moves between quantum dots and nearby molecules. The proton briefly shifts position, helps coordinate ...