Motion sensors play a vital role in the Internet of Things (IoT). In fact, the smart home simply can’t exist without smart sensors, so their significance can’t be understated. With their ability to detect movement, intrusion and occupancy, these sensors are essential to enabling devices — thermostats, lights, home security solutions, etc. — to react and interact with one another.
Not surprisingly, the market for motion sensors is thriving. Gartner projects there will be 25 billion connected devices by 2020, and ABI Research forecasts shipments for motion sensors in particular will have a compound annual growth rate (CAGR) of 71.2 percent from 2011 to 2018.
Those aren’t exactly figures to sneeze at. And everyone, it seems, is rushing to converge devices in ways that improve the comfort, security and convenience of everyday life.
Now You See it, Now You Don’t
While most human eyes can’t see in the dark, passive infrared (PIR) motion sensors see a glow from everything. Most humans only see with the presence of visible light reflecting off of objects, but PIR sensors see the infrared (IR) glow of objects in the dark as clearly as we see in daylight because these objects emit IR light. This means they can easily be employed to activate lighting or report intruders, providing real-time detection at a fraction of the cost of any camera. As a result, smart homes can be smart 24/7, at an affordable price point.
That said, to get maximum effect from PIR sensors you have to think it through, because the devil is in the details and the technology out there varies widely.
The Value of PIR Motion Sensors
In homes, PIR motion sensors serve two main purposes: occupancy detection and intrusion detection. While equally important, both sensor applications have different sensibilities.
Occupancy-related sensors provide many small fields of view; they identify a person’s presence by detecting minor human body motions entering or leaving any of the small fields of view. It’s all about efficiency. Smart homes can conserve energy and lower their bills if their thermostats, lights, TVs and other energy-consuming devices are able to react to occupancy sensors. These sensors notice all the small stuff so consumers can save money as they reduce their overall energy footprint.
The other main purpose for PIR motion sensors is intrusion detection. Everyone wants to know if there’s an intruder at the door or inside their home, but no one wants Fido tripping the sensors every time he goes to his food bowl or ambles into the study for his favorite toy. This means intrusion detection sensors must be architected to ignore minor motion like pet movements and non-moving objects of changing temperature. Intrusion sensors must be able to distinguish pets from people by size, not only by relative IR signal strength (which can vary by floor/wall temperature, pet hair length, etc.).
In addition, high-quality intrusion sensors should employ at least quad-element IR detectors that can support features such as multi-signal phase offset. Phase offset confirms motion, avoiding false triggers by IR light changes that are not caused by a moving person.
Unfortunately, many IR detection sensors have not been optimized for either occupancy detection or intrusion detection. And, most that are specialized to meet the needs of one area often don’t meet the needs of the other; this means that two separate sensors are required. Occupancy-sensing (lighting control) sensors often can be too sensitive for security-system use, and give frequent false alarms caused by pets when no one is home, while intrusion-sensing (security system) sensors usually are not sensitive enough for consistent detection of sedentary occupants in a room.
So, if you want both occupancy detection and intrusion detection at an affordable price point, you really need to take a good long look at the motion sensor technology itself.
What’s on the Inside Counts
In contemporary smart home systems, it has been common for companies to use low-performance devices for IR detection to drive device cost down. While cost considerations should play a part in the decision, if you want great motion detection, few false alarms and a long-lasting system, simply choosing a low-performance device for IR detection probably isn’t your best bet.
- Here is a list of key features to look for in any PIR sensor technology you’re considering:
- A dense field of view (FOV) pattern (the denser this is, the more it will be able to detect small movements)
- Pet immunity (to reduce false alarms)
- Long battery life (high-quality PIR sensors can last multiple years on one battery)
- High-count lens array (the higher the number of individual lens elements, the more FOVs there will be)
- High number of detector elements — for example, quad-element versus dual-element (the more there are, the more FOVs there will be)
Now, it’s important to note that recent advances in PIR technology have resulted in some new 2-in-1 PIR motion sensors that provide both a pet-immune intrusion detection signal (when people are away from home) as well as a sensitive occupancy detection signal (for smart, convenient and energy-efficient lighting/climate control when people are at home).
Capitalizing on the convergence trend and combining two sensor functions should pave the way for a raft of consumer solutions that offer the security function and the generalized smart home function in a single convenient device. Interoperability is key in IoT, so it only makes sense that the main ingredient of your smart home recipe communicates and functions as efficiently as possible.
The bottom line is that the positive global impact of PIR sensors will be enormous. Smart home systems provide an ideal use case because they cannot function without smart sensors. The concept of the smart home is undoubtedly exciting, but the buzz breaks down if all your connected devices don’t communicate as effectively as they’re designed to.
That’s exactly why high-quality sensor performance enhances the entire smart home environment. Assuming the industry can continue pushing forward fast and can get everything needed into a very small form factor (which is already starting to happen), who wouldn’t want an easy-to-use and cost-effective solution that could improve their personal safety while at the same time reduce their energy consumption, and enhance climate control in their home?
Funny, I can’t think of anyone either… and that’s why I’m betting that ever-improving PIR sensors will help accelerate mass adoption of IoT.
Eric Micko is director of hardware design at Greenwave Systems.