{"id":1017,"date":"2026-02-19T21:35:32","date_gmt":"2026-02-19T13:35:32","guid":{"rendered":"https:\/\/pirhome.com\/?p=1016"},"modified":"2026-02-19T21:35:32","modified_gmt":"2026-02-19T13:35:32","slug":"pir-behind-glass","status":"publish","type":"post","link":"https:\/\/www.pirhome.com\/?p=1017","title":{"rendered":"PIR Sensor Behind Glass: Does It Work?"},"content":{"rendered":"<h2>The Short Answer<\/h2>\n<p>No, a standard PIR sensor will not work reliably behind glass. Glass is opaque to the mid-infrared wavelengths (8-14 \u03bcm) that PIR sensors detect.<\/p>\n<h2>Why Glass Blocks Infrared<\/h2>\n<p>Ordinary glass (soda-lime glass) is transparent to visible light but strongly absorbs thermal infrared. This is why greenhouses stay warm\u2014they trap infrared inside. For a PIR sensor behind glass, the infrared from a warm body outside is absorbed by the glass and never reaches the sensor.<\/p>\n<h2>What About Special Glass?<\/h2>\n<p>Some materials, like germanium, silicon, or certain plastics (polyethylene), are transparent to IR. However, standard window glass is not. Even &#8220;low-E&#8221; glass, designed to reflect IR, will block it.<\/p>\n<h2>Can I Use a PIR Through a Window If&#8230;<\/h2>\n<ul>\n<li><strong>&#8230;the window is open?<\/strong> Then yes, the sensor can see through the opening.<\/li>\n<li><strong>&#8230;I remove the glass?<\/strong> Then it&#8217;s not behind glass anymore.<\/li>\n<li><strong>&#8230;I use an IR-transparent window?<\/strong> If you replace the glass with a material like polyethylene film, it might work, but this is impractical for most.<\/li>\n<\/ul>\n<h2>Alternatives for Through-Window Detection<\/h2>\n<p>If you need to detect motion outside from inside:<\/p>\n<ol>\n<li><strong>Microwave\/Radar Sensor<\/strong>: These use radio waves that penetrate glass easily. Sensors like RCWL-0516 can detect motion through walls and windows.<\/li>\n<li><strong>Dual-Technology Sensor<\/strong>: Some units combine PIR and microwave; the microwave part works through glass.<\/li>\n<li><strong>External Sensor<\/strong>: Mount the PIR outside, in a weatherproof housing, and run wires inside.<\/li>\n<li><strong>Acoustic\/Ultrasonic<\/strong>: Not typically used for through-glass, but possible.<\/li>\n<\/ol>\n<h2>What About Car Windows?<\/h2>\n<p>Automotive glass often has coatings that further block IR. Even without coatings, the glass itself blocks IR. A PIR sensor inside a car will not detect someone outside unless the window is down.<\/p>\n<h2>Testing for Yourself<\/h2>\n<p>If you want to verify, place a PIR sensor behind a closed window and try to trigger it from outside. You&#8217;ll likely get no response, or very erratic triggering if the glass is thin and the sun is strong (the sensor may detect the sun&#8217;s heating of the glass itself).<\/p>\n<h2>Conclusion<\/h2>\n<p>For reliable motion detection, do not rely on a PIR sensor behind glass. Choose a different technology or mount the sensor outside.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>The Short Answer No, a standard PIR sensor will not work reliably behind glass. Glass is opaque to the mid-infrared wavelengths (8-14 \u03bcm) that PIR sensors detect. Why Glass Blocks Infrared Ordinary glass (soda-lime glass) is transparent to visible light but strongly absorbs thermal infrared. This is why greenhouses stay warm\u2014they trap infrared inside. For [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[],"class_list":["post-1017","post","type-post","status-publish","format-standard","hentry","category-troubleshooting"],"blocksy_meta":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.3 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\r\n<title>PIR Sensor Behind Glass: Does It Work? - PIRHOME<\/title>\r\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\r\n<link rel=\"canonical\" href=\"https:\/\/www.pirhome.com\/?p=1017\" \/>\r\n<meta property=\"og:locale\" content=\"en_US\" \/>\r\n<meta property=\"og:type\" content=\"article\" \/>\r\n<meta property=\"og:title\" content=\"PIR Sensor Behind Glass: Does It Work? - PIRHOME\" \/>\r\n<meta property=\"og:description\" content=\"The Short Answer No, a standard PIR sensor will not work reliably behind glass. Glass is opaque to the mid-infrared wavelengths (8-14 \u03bcm) that PIR sensors detect. Why Glass Blocks Infrared Ordinary glass (soda-lime glass) is transparent to visible light but strongly absorbs thermal infrared. This is why greenhouses stay warm\u2014they trap infrared inside. 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