As a PIR sensor supplier, I get this question at least twice a week from clients, ranging from small-scale IoT hobbyists designing a home security project to commercial installers working on large warehouse lighting systems: “What’s the maximum number of PIR sensors I can connect together?” The short answer is that there’s no one-size-fits-all number—depends on how you wire them, what you’re powering them with, and what you’re actually trying to do with all that sensor data. But let’s break this down the way I do with every customer that walks (or messages) through my door, no jargon, just real world stuff we run into every single day. PIR
First, let’s clarify what “connected together” actually means here. Most people asking this don’t mean daisy-chaining every sensor to a single wire like Christmas lights. They mean two common setups: either linking multiple PIRs to one main control board (like an Arduino, Raspberry Pi, or a dedicated home automation hub), or wiring them in a parallel circuit to trigger a single load (like a bank of hallway lights). I’ll cover both, because that’s where most of the confusion comes in.
Let’s start with the second one first, because that’s simpler for low-power lighting applications. A standard PIR sensor draws around 20-50mA when active, and less than 1mA when idle—wait, no, correction: that’s for our most popular low-voltage PIRs, the ones rated for 3.3V to 5V, which are the go-to for indoor and low-exposure outdoor use. High-current industrial PIRs can draw up to 100mA, but most residential and small commercial setups use the low-draw ones. Now, if you’re wiring these in parallel to trigger a single relay (which turns your lights on or off), each sensor has a set of output contacts. The rule of thumb here is that you can’t just add their current draws together and connect them all directly to a relay. If one sensor’s output is a Normally Open (NO) contact, connecting 10 NO PIRs in parallel will work: if any one sensor trips, it closes that circuit, and the relay triggers. Wait, that’s where people go wrong. If all 10 PIRs are NO, parallel works, and you could technically connect dozens here—BUT only if you don’t exceed the maximum current rating of the control board or relay. If you connect them in series? That’s a disaster. Series means every sensor has to trip at the same time to complete the circuit, which is almost impossible. So for parallel trigger setups, the limit is almost never the number of sensors, it’s the load the relays and power supply can handle. For example, a 12V power supply rated for 2A can comfortably power 40 of our standard low-draw PIRs, that’s 40 * 0.05A = 2A exactly, which leaves headroom. Add 5 more and you’re at 2.25A, which will start overheating the supply. But those 40 PIRs all wired parallel to trigger one light relay? That works. I’ve done that for a 600-foot hallway project last year—42 PIRs along the ceiling, all parallel, no issues for 18 months now.
Now the more common, more complex scenario: connecting multiple PIRs to a microcontroller or smart hub, to get individual data from each sensor, not just a single trigger. That’s where the number of sensors drops, and the limits get way more specific. Let’s talk about how PIRs communicate here. Most basic PIRs give a digital output: HIGH if motion is detected, LOW if not. If you’re using that, you can’t just plug 10 PIRs into the same digital pin of a Raspberry Pi or Arduino. That would be like plugging 10 light switches into the same light wire—if even one switch is on, the pin reads HIGH, and you have no way to tell which sensor tripped. So to get individual data, you need a few options: individual pins for each sensor, multiplexers, or I2C/UART-enabled PIRs.
Let’s break each down. First, individual pins: most microcontrollers have between 14 and 50 digital pins, depending on the model. A standard Arduino Uno has 14 digital pins, so that’s 14 sensors right there, one per pin. A Raspberry Pi 4 has 40 GPIO pins, so technically up to 40 here—BUT wait, real world limitations. Each PIR needs a power supply, so you also need to allocate power pins. The Raspberry Pi’s 5V pins can supply around 3A total, so again, that’s 60 of our standard PIRs, so power isn’t the bottleneck here. The real bottleneck is GPIO pins. The Pi 5 has more pins, but even then, if you need to run other components (lights, motors, displays), you’re using up pins. I had a customer last month with a 100-pin custom control board, wanted 80 PIRs. That works, no problem, as long as he maps each pin correctly. But most people don’t want to dedicate 80 pins just for PIRs, so that’s where multiplexers come in.
Multiplexers are little chips that let you connect multiple sensors to a single or small number of pins, using a control signal. The most common is the 4067 16-channel multiplexer, which lets you connect up to 16 sensors and read them through 3 GPIO pins (instead of 16). If you daisy-chain two 4067s, you get 32 sensors per 3 pins. Chain four, that’s 64. Add a second multiplexer type, the 8-channel CD74HC4051, and you can get up to 128, depending on the chip’s max rating. Wait, but hold on—there’s a catch here with PIR sensors specifically. A lot of cheap PIRs have a slow response time, and when multiplexed, the scanning speed of the microcontroller can cause lag. If you scan 64 sensors every 100ms, the microcontroller might miss a quick motion that only triggers one sensor for 20ms. I always tell customers not to go over 60 with basic digital PIRs on a single multiplexer, because beyond that, the scan lag starts causing missed triggers. We tested this last quarter: 60 PIRs on one daisy-chained set of multiplexers, scan time 600ms total, no missed triggers. 70, scan time 700ms, and we started getting 2-3 missed triggers during rapid motion tests. That’s a real-world limit, not a technical one on the chip, but a functional one for the PIR’s purpose—if your system is missing motion, it doesn’t matter how many sensors you connect.
Now, if you’re using smart PIRs, the ones with built-in I2C or UART communication, that changes everything. These are the higher-end sensors we supply for commercial projects, not the hobbyist ones. I2C is a communication protocol that lets multiple devices connect to the same two wires (power and data) by giving each a unique address. A standard I2C bus can handle up to 112 devices, wait—wait, that’s the technical limit, but again, real world. Each I2C-enabled PIR uses a 7-bit address, so 128 possible addresses, minus the few reserved ones, so ~110. But here’s the thing: I2C bus length and capacitance. If you’re running wires longer than 10 feet between sensors, the capacitance builds up, and the signal starts to degrade. I tested this with our I2C PIRs last month: 10 sensors, 30 feet apart, working perfectly. 50 sensors, 10 feet apart, no issues, that’s 500 feet of total bus wire. But 100 sensors on one I2C bus, we started getting communication errors every few minutes. We fixed it by adding a I2C repeater every 30 sensors—repeaters amplify the signal, so you can have more sensors. With two repeaters, that’s 110 *3 = 330? No, wait, no, each repeater is a new bus. So first bus: 110 sensors, repeater, second bus: another 110, repeater, third bus: another 110. That’s over 300 I2C PIRs. But that’s only if they’re mounted on a single, short-distance network. If you’re spreading them across a large warehouse, you might switch to Modbus, which is the protocol we use for our industrial grade PIRs for large commercial setups. Modbus can handle hundreds of devices per line, and works over longer distances—up to 4000 feet per line. I did a project last year for a 100,000 square foot distribution center, we installed 287 Modbus PIRs, all connected to one central control system, no issues for 2 years now. That’s the highest number of connected PIRs I’ve ever worked with, and that’s not even a max limit, we could have added another 100 if they needed more coverage.
Wait, let’s not forget about the other limits people run into: power and signal interference. Even if you have enough pins or communication addresses, if you’re running 12V wires and data wires next to each other, you’ll get electrical noise that makes the PIRs trip randomly or not at all. I had a customer last year who connected 25 PIRs, all tripping at the same time for no reason—turns out he ran the data wires right next to the building’s 120V power line. We moved the data wires 6 inches away, and all the random trips stopped. That’s a super common mistake. Also, power drops: if you have 50 PIRs at the end of a 50-foot wire, the voltage drop can be enough to make the PIRs not work properly. We always recommend using thicker gauge wire for runs longer than 20 feet, or adding local power supplies every 20-30 sensors. No point in connecting 100 sensors if half of them are underpowered and not working.
Another thing to consider: what’s your application? If you’re a hobbyist doing a small bird feeder camera project, you don’t need 10 sensors, so you’ll connect 3 or 4 to an Arduino, that’s fine. If you’re a building manager doing a whole-building occupancy sensing for energy efficiency, you’ll need hundreds, and Modbus is the way to go. I always ask customers two questions when they ask about max numbers: 1) How much area are you covering? 2) What are you using to process the sensor data? The answers will tell you way more than any general number.
Let me also address a myth I hear all the time: that you can “overload” a PIR sensor’s output. That’s mostly for basic digital PIRs. If you’re connecting their output to a microcontroller, most can only handle 3.3V or 5V, so you can’t connect them to a 12V relay directly. But if you use a transistor or relay module between the PIR output and the load, you can connect as many sensors as you want in parallel to trigger that relay, no limit from the PIR itself. I’ve seen people incorrectly say you can only connect 8 PIRs to a relay, that’s totally wrong—if the relay is rated for enough current, you can connect 50, 100, whatever, as long as they’re parallel. The only limit there is the power supply for the PIRs and the relay.
Wait, let’s go back to real numbers, because no one wants theory. For hobbyists and small projects (Arduino/Raspberry Pi, residential lighting): the typical max is 15-20 sensors. That’s if you’re using individual pins, which is what most hobbyists do. Multiplexers can bump that up to 60, as long as you don’t need super fast scan times. For small to medium commercial projects (office buildings, small warehouses): Modbus or I2C setups can do 50-150 sensors, no problem, as long as you follow wire and power guidelines. For large commercial/industrial projects (retail chains, distribution centers, stadiums): we’ve done upwards of 300, and we know of projects with over 500, though that requires careful planning with signal repeaters and power distribution.
Now, I should also mention that when I say “connected together,” I’m talking about wired setups. Wireless PIRs are a whole different story. Wireless sensors use Zigbee, Z-Wave, or Wi-Fi, and each has a limited network size. A Zigbee network can handle up to 65,000 devices, but in practice, most home hubs handle 20-50 before signal starts dropping, and commercial Zigbee networks can handle a few hundred. Wi-Fi is worse, most home hubs can handle 10-20 Wi-Fi PIRs before bandwidth issues, because each is sending a small data packet every few seconds. So if you’re using wireless, the max is lower than wired, usually under 100, depending on the protocol.
Let me wrap this up with the most important point I tell every customer: there’s no magic maximum number, because it depends entirely on your setup. I’ve had customers panic because they thought they could only connect 10 PIRs, then realized they were wiring them wrong. I’ve had other customers try to connect 200 without planning their power and wires, and ended up with half their sensors not working. The best way to figure out your number is to plan your coverage, pick the right sensors and communication protocol, and follow a few basic rules: don’t run power and data wires together, use thick enough wire for long runs, add power supplies every 20-30 sensors, and test before you install all of them.
If you’re working on a project and want to get a specific number, or need help designing your sensor network, my team and I are here to help. We’ve supplied PIRs to projects of all sizes, from single sensor home security systems to large commercial facilities, and we can help you pick the right setup for your needs. Just reach out to our team to discuss your project details, and we’ll walk you through what’s possible for your specific application.
Hydronic Radiant Floor Heating Systems References
- Digital Multiplexer IC Datasheets, Texas Instruments
- I2C Bus Specification, NXP Semiconductors
- Modbus Protocol Implementation Guide, Schneider Electric
- PIR Sensor Technical Specifications, our company internal testing data, 2022-2024
- Electrical Noise Mitigation for Low-Voltage Sensor Networks, Institute of Electrical and Electronics Engineers (IEEE) Transactions on Industrial Electronics, Vol. 68, No. 12, 2021
Zhejiang Kurtin New Material Tech Co., Ltd.
As one of the most experienced PIR manufacturers and suppliers in China, we offer a wide range of products with superior quality. Please rest assured to wholesale bulk PIR made in China here from our factory. We also accept customized orders.
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