The Right Moves in Motion Sensing

Dissecting this most delicate of technologies

They may be over sixty years old, but motion sensors (MS) are still on the cutting edge of technology. From their use in automation to measuring human health, this technology is shaping (and improving) our lives. Activity detection has also been evolving when it comes to security; so much so that motion alone is no longer the only means used to detect unwanted visitors on your premises.

There are a number of different types of motion sensors on the market based upon active and passive performance principles. Here’s a look at what they are, the way they operate, and how they match up against each other.

Passive infrared sensor (PIR)

PIR is also referred to as IR motion or pyroelectric. It takes the passive part of its name by emitting no energy of its own; rather, PIR detects external energy via a pyroelectric sensor and reacts accordingly. All living things emit infrared radiation in the form of body heat. As such, any individual who enters a room will raise the amount of infrared in the surrounding environment (over and above the ambient energy of the space). Their movement will be registered by the PIR.

To its advantage, PIR is a relatively low-cost technology with low power consumption and a wide field of vision. It can also operate in darkness as effectively as light. A disadvantage here is the possibility of over-sensitivity. This problem is usually overcome by the PIR’s make-up which consists of sensors in its face that need to be triggered sequentially. This helps prevent PIR from false alarms caused by sunlight, temperature changes, or vibration.

Active motion sensors (AM)

Contrary to passive models, active sensors (also called microwave sensors) emit radar waves or infrared energy in order to detect unwanted entrants. AMs gather their data by judging the time the emitted waves take to return. In an empty room, the returning waves will have a regular return cycle. An intruder will interrupt this regularity and trigger an alarm.

The advantages of AMs are their long lifecycle and ability to function in areas where a passive sensor might fail, such as high-temperature environments. AMs can fail where PIRs succeed, however. Active sensors may be prone to false alarms by wind or certain types of light. AMs may be overcome due to operating at irregular intervals caused by greater power consumption. If an intruder can ascertain their cycle, then they may slip in undetected.

Ultrasonic sensors (US)

The US may be classified as an active sensor, but instead of emitting infrared or radar to detect intruders, it utilizes sound waves. US tech “listens” to how long it takes the echo of its sound to return. Objects in their usual places will return non-threatening signals. Anything moving around which shouldn’t be will raise a red flag. The accuracy of US can be affected by humidity and temperature, as well as by certain fabrics and varying object size.

Combined motion sensors (CMS)

This form of motion sensor couples both active and passive approaches to recognize of intruders. Each tech draws on the other’s strengths to minimize their weaknesses: CMS typically remain on the passive (and thusly lower energy) settings until unwanted activity is suspected. The active/microwave component is then activated rather than having it consume power through constant signal emission. If both segments of the sensor detect trouble, they will trigger an alarm.

How to overcome every potential sensor failure

Even the most sensitive technology can be prone to error. If you’re serious about maximizing the efficiency of your security, it pays to include a human element. A remote monitoring team can not only oversee any triggered alarms for their veracity, they can keep a close check on who is entering and leaving the building at all times while securing doors, verifying visitor ID’s, and alerting business owners and law enforcement to any suspicious party or activity.

We offer more information about remote monitoring in our free guide. You, your premises or your business are unique and so is the security solution that is perfect for you. If you’re considering any form of security protection, we’re the professionals to consult for lasting peace of mind.

Since 2002, Peace of Mind Technologies has delivered over 2,000 security solutions across six industries in the greater New York Metropolitan area. We’re specialists who work with your team to provide comprehensive site-specific security from implementation to post-installation support. To discuss your needs with the experts, call us at (212) 688-2767, email us at, or complete our contact form for a free consultation.