Introduction
The PIR sensor is one of the most successful electronic sensors ever invented. Billions are in use worldwide. But where did it come from? Let’s trace its history from冷战-era military research to today’s smart homes.
The Physics Foundation: Pyroelectricity
The pyroelectric effect was first observed in ancient times (Theophrastus noted that tourmaline attracts straw when heated). But it wasn’t until the 19th century that scientists like Brewster and Lord Kelvin studied it systematically. The term “pyroelectricity” was coined by Brewster in 1824.
Early 20th Century: Military Applications
During World War II, infrared technology advanced for night vision and missile guidance. However, practical motion detection based on pyroelectricity remained in labs.
1950s-1960s: The Birth of Modern PIR
In the 1950s, researchers developed sensitive pyroelectric materials like triglycine sulfate (TGS) and later lithium tantalate. These made practical infrared detectors possible.
The first passive infrared intrusion detector was patented in the early 1960s. These early systems used cooled detectors and were bulky and expensive, used only in high-security military sites.
1970s: Commercialization
The invention of the dual-element pyroelectric sensor (to cancel common-mode signals) was a breakthrough. Companies like Eltec (now part of Panasonic) and Murata began producing small, uncooled pyroelectric detectors.
By the late 1970s, PIR sensors started appearing in commercial security systems, replacing less reliable ultrasonic and microwave detectors. They were still relatively expensive.
1980s: The HC-SR501 Era Begins
As manufacturing costs dropped, PIR sensors became affordable for consumer applications. The HC-SR501 module (or its clones) emerged as a de facto standard for hobbyists. It combined the pyroelectric sensor, a Fresnel lens, and support circuitry on a small board.
1990s-2000s: Ubiquity
PIR sensors became ubiquitous: automatic lights, security systems, occupancy sensors for energy-saving lighting. The technology matured with improved lenses, digital outputs, and lower power consumption.
2010s: IoT and Smart Homes
The Internet of Things (IoT) revolution created massive demand for low-power motion sensors. PIR sensors were integrated into smart home devices like Philips Hue motion sensors, Ring security cameras, and countless DIY projects with ESP8266/Arduino.
2020s: Competition from mmWave
mmWave radar emerged as a competitor, offering presence detection (not just motion). However, PIR remains dominant due to its low cost and simplicity. Hybrid sensors combining PIR and mmWave are appearing.
The Future of PIR
PIR sensors will likely remain the workhorse for simple motion detection. Advances include:
- Even lower power (sub-µA) for energy harvesting
- Digital interfaces (I2C, SPI) for configuration
- Integrated analytics (people counting, direction detection)
- Smaller SMD packages for wearables
Conclusion
From military labs to your smart light switch, the PIR sensor has had a remarkable journey. Its simplicity, reliability, and low cost ensure it will be with us for decades to come.