Supply Voltage & Idle Current

The HC-SR501 and HC-SR505 have an onboard regulator and want about 5V or more. The AM312 runs straight from 3.3V and idles in the micro-amp range, which matters for coin-cell and deep-sleep nodes. Radar modules draw milliamps, not micro-amps.

Range & Field of View

The large 23mm dome on an HC-SR501 covers roughly 3–7 m in a wide cone. Mini PIRs like the AM312 and HC-SR505 reach about 3 m. Pick the shortest range that covers your area to cut false triggers.

Adjustable Timing

The HC-SR501 has two potentiometers (sensitivity and hold time) plus a single/repeat trigger jumper. Mini modules have a fixed hold time, which is fine when your firmware handles timing anyway.

Output Type & Logic Level

PIR and RCWL-0516 modules give a simple 3.3V-high digital output, safe for ESP32, Pico and Raspberry Pi GPIO without a level shifter. The LD2410C adds a UART stream with distance and moving/still target data.

PIR vs Radar

PIR is cheap, frugal and ignores anything that isn’t warm. Microwave radar sees through plastic and wood but also through thin walls. mmWave presence radar detects breathing-level micro-motion, so it knows a still person is still there.

Not a PIR, but the answer to PIR’s biggest weakness. The LD2410C is a 24GHz FMCW radar that picks up the micro-motion of breathing, so it keeps reporting a person sitting at a desk or lying in bed long after a PIR would have timed out. You get a simple presence output pin plus a UART stream (256000 baud by default) with separate moving and stationary target states and approximate distance, and you can tune per-distance-gate sensitivity over Bluetooth with the HLKRadarTool app. It is well supported by the ESPHome LD2410 component and Arduino libraries, which makes it a favourite for Home Assistant room-occupancy sensors.

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The RCWL-0516 is a microwave Doppler motion sensor that wires up exactly like a PIR (VIN, GND, OUT) but works in a completely different way. Because it doesn’t need a line of sight for infrared, it detects through plastic, wood and glass, so you can hide it inside a sealed project box with no lens hole. It accepts a very wide 4–28V input, outputs a 3.3V logic HIGH, draws only a few milliamps and even provides a regulated 3.3V output pin for small loads. A CDS pad lets you add a light sensor so it only triggers in the dark. We have full guides for using it with the ESP32 and ESP8266.

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Stemedu’s listing focuses on the HC-SR501’s 4.8–20V wide input, which means you can power it directly from the 12V rail of an LED strip controller, alarm panel or automotive project without a separate 5V regulator. It exposes both trigger modes through a jumper (repeat trigger is the default), adjustable delay of roughly 0.5–200 s and a separate block time, plus a 100° cone through the standard 23mm lens. Stemedu also links to MySensors documentation from the listing, which is handy if you’re building a home-automation node.

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A bare HC-SR501 dangling from jumper wires looks unfinished and is easy to knock out of alignment. WWZMDiB’s five-pack is the same adjustable 4.5–20V PIR with a 3–7 m range and both H (retrigger) and L (single trigger) modes, but it adds two dedicated cases so you can wall- or ceiling-mount a couple of sensors neatly. That makes it a good fit for a hallway light, a doorway counter or a garage alert where the sensor will stay in place for years.

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The HC-SR505 is a pencil-thin, cylindrical PIR that drops into a small hole in a panel or 3D-printed housing. Like the HC-SR501 it uses a regulator, so it is happiest on 5V or higher (the listing quotes 4.5–20V), and it outputs a 3.3V HIGH when it sees motion. There are no pots: range is roughly 3 m and the hold time is fixed, so it suits simple “turn on when someone approaches” jobs like cabinet lights or a desk display wake-up. We’re including it because so many readers ask about it, but note its 3.9-star Amazon rating is the lowest in this guide; buy a multi-pack and test each unit.

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Building an alarm or automatic light?

Start with the DIYmall HC-SR501 5-pack: adjustable range and hold time, and plenty of spares.

Running on batteries or 3.3V?

Use the HiLetgo AM312 as a deep-sleep wake source on ESP32, nRF52 or Pico.

Need to know someone is still in the room?

Choose the LD2410C mmWave radar. It detects seated and sleeping people that PIRs miss.

Sensor must hide inside a sealed box?

The RCWL-0516 microwave sensor works through plastic with no lens hole.

Powering from a 12V LED or alarm rail?

Go for the Stemedu wide-voltage HC-SR501, or the WWZMDiB pack if you want cases too.

Panel-mounting in a small 5V device?

The slim HC-SR505 fits through a small hole and needs no configuration.

What is the difference between the HC-SR501, AM312 and HC-SR505?

All three are passive infrared sensors with a 3.3V digital output. The HC-SR501 is the largest, with a big dome lens, about 3–7 m range and potentiometers for sensitivity and hold time; it needs roughly 5V or more. The AM312 is a tiny module that runs directly from 3.3V with micro-amp idle current but has fixed settings and about 3–5 m range. The HC-SR505 is a slim cylindrical version with fixed settings and roughly 3 m range that, like the SR501, prefers 5V or higher.

Can I connect a PIR sensor directly to an ESP32 or Raspberry Pi?

Yes. The output of these modules swings to about 3.3V, which is safe for ESP32, ESP8266, Raspberry Pi Pico and Raspberry Pi GPIO pins without a level shifter. Power the HC-SR501 or HC-SR505 from the 5V pin and the AM312 from 3.3V, connect grounds together and read the OUT pin as a digital input or interrupt. See our ESP32 PIR interrupt tutorial and PIR with Raspberry Pi Pico guide for wiring and code.

Why does my PIR sensor trigger randomly or stay HIGH?

The most common causes are the power-on warm-up (ignore the output for the first 30–60 seconds), sensitivity set too high, a long hold time that makes it look stuck, heat sources such as sunlight, heaters or air vents in the field of view, and electrical noise. Noise from a nearby Wi-Fi antenna or a weak supply is a frequent culprit on ESP32 builds: add a 100 µF capacitor across the sensor’s supply pins, keep the sensor a few centimetres from the antenna and turn the sensitivity pot down.

Should I use a PIR or a radar sensor like the RCWL-0516 or LD2410C?

Use a PIR when you want the lowest cost and power and only need to detect people moving through a space. Use an RCWL-0516 when the sensor must be hidden behind plastic or when heat sources fool your PIR, accepting that it can also see through thin walls. Use an LD2410C when you need true occupancy, meaning it should keep reporting someone who is sitting or sleeping. Many smart-home builders combine a PIR for fast trigger with an LD2410C for reliable hold-on.

Can a PIR sensor wake an ESP32 from deep sleep?

Yes, and it is one of the best uses for one. Connect the PIR output to an RTC-capable GPIO and configure it as an external wake-up source (ext0 or ext1). The ESP32 sleeps at micro-amp current until motion is detected, does its work (send a notification, take a photo) and goes back to sleep. An AM312 is ideal here because it runs from 3.3V and adds almost nothing to the sleep current. Our ESP32 deep sleep wake-up sources tutorial shows how.