SDK and documentation for 60GHz mmWave radar sensors.
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Millimeter wave radar detects human presence, breathing, heart rate, body movement, and sleep stages without any physical contact. It does not need a camera, and the person does not need to wear anything. This makes it a practical sensing technology for homes, elderly care, hotels, and offices.
This article explains how millimeter wave radar works, starting from the FMCW principle, and why the 60GHz band is able to detect chest movement smaller than one millimeter. It also compares millimeter wave radar with PIR sensors, cameras, and wearable devices.
Millimeter wave refers to electromagnetic waves with a wavelength between 1 mm and 10 mm, which corresponds to a frequency range of roughly 30 GHz to 300 GHz. It is simply a segment of the electromagnetic spectrum, in the same way as infrared or visible light.
Millimeter wave has three useful properties for indoor sensing:
For indoor presence detection, sleep monitoring, and fall detection, 60 GHz is the most widely validated and cost-effective choice. At 60 GHz the wavelength is approximately 5 mm, which is short enough to build a compact antenna array and fine enough to resolve small targets.
Most indoor millimeter wave sensors use FMCW (Frequency Modulated Continuous Wave). Instead of sending a short pulse, the radar transmits a continuous signal whose frequency sweeps linearly up and down over time. The processing chain has five steps.
The radar transmits a 60 GHz FMCW chirp through its antenna array. Because the wavelength is only about 5 mm, the antenna can be small enough to fit inside a ceiling-mounted housing.
The wave hits the target and part of the energy is reflected back. The echo carries information about range, velocity, and angle. A human chest reflects the signal continuously, even when the person is completely still, because breathing moves the chest wall.
The received echo is mixed with the transmitted signal. The mixing produces a beat frequency that is proportional to the target range. The signal is then filtered and sampled by an ADC.
An FFT separates targets in the range domain, and Doppler and phase differences reveal velocity and micro-movement. This is the step that separates a real human from a moving curtain: a curtain has movement but no stable phase structure or breathing rhythm.
The processed result is published as application data: presence status, body movement level, human distance, breathing rate, heart rate, sleep stage, or fall alarm.
Breathing moves the chest wall by less than 1 mm. Detecting this requires very fine range resolution and a stable phase reference, and this is where the 60 GHz band performs well.
The reasons:
For comparison, the 24 GHz band has a wavelength of about 12.5 mm, which makes it less sensitive to micro-motion and requires a larger antenna. 24 GHz radar is well suited to presence detection over a wide area, while 60 GHz radar is the better choice when breathing, heart rate, or sleep stages are required.
| Signal | What It Measures | Typical Range | Report Frequency |
|---|---|---|---|
| Human presence | Occupied / unoccupied | Up to several meters | On change |
| Motion status | Static / active | — | On change |
| Body movement | Movement level 0–100 | — | Every 1 s |
| Human distance | 0–65535 cm | Non-critical function | Every 2 s |
| Breathing rate | 0–45 breaths/min | ~1.5 m | Every 3 s |
| Heart rate | 50–120 bpm | ~1.5 m | Every 3 s |
| Sleep stage | Awake / light / deep | ~2.5 m | Every 10 min |
| Sleep score | 0–100 | — | On sleep end |
| Fall alarm | Fall detected | ~2.5 m | On change |
| Dwell alarm | Static dwell detected | ~2.5 m | On change |
The movement parameter is reported as a value from 0 to 100, with fixed meaning:
| Value | Meaning |
|---|---|
| 0% | No person in range |
| 1% | Still (breathing only, no limb movement) |
| 2%–30% | Micro movement (small head or limb motion) |
| 31%–60% | Walking or fast limb movement |
| 61%–100% | Running or large close-range movement |
While a person is in bed, the radar evaluates the sleep stage every 10 minutes and reports awake, light sleep, or deep sleep. When the sleep session ends, it reports a sleep score from 0 to 100:
| Score | Rating |
|---|---|
| 1–60 | Poor |
| 61–75 | Fair |
| 76–100 | Good |
The sleep report includes total sleep duration, awake / light / deep percentages, time out of bed, number of times out of bed, turn count, average breathing rate, average heart rate, and apnea count.
The radar also reports sleep anomalies:
| Technology | Detects a Stationary Person | Works in Darkness | Measures Breathing | Privacy Risk | Wearing Required |
|---|---|---|---|---|---|
| PIR sensor | No | Yes | No | None | No |
| Camera | Yes | Needs infrared | No | High | No |
| Wearable device | Yes | Yes | Yes | Low | Yes |
| mmWave radar | Yes | Yes | Yes | None | No |
A PIR sensor only reacts to movement, so a person sitting still or sleeping is invisible to it. A camera captures images, which raises privacy concerns in bedrooms and bathrooms and needs infrared illumination in the dark. A wearable device measures breathing well, but it must be worn and charged, and many users stop wearing it after a few weeks.
Millimeter wave radar has none of these limitations, and it produces no image data at all. The output is a set of numbers.
Millimeter wave passes through most non-metallic materials. It also reacts to any movement inside the detection area.
Penetrates without affecting detection:
Causes interference or false alarms:
Note: Do not aim the radar directly at an air conditioner, or install it facing the same direction as the air flow. The internal motor causes false detection.
| Misconception | Reality | Solution |
|---|---|---|
| “It is just a motion sensor” | It resolves chest displacement below 1 mm through phase analysis | Aim the main beam at the chest area |
| “60GHz and 24GHz are the same” | 60GHz is far more sensitive to micro-motion and needs a smaller antenna | Use 60GHz for breathing, heart rate, and sleep |
| “Higher sensitivity is always better” | High sensitivity picks up curtains, fans, and pets | Match sensitivity to room size and interference |
| “It cannot work through a blanket” | Non-metallic materials do not block the signal | Keep metal away from the antenna face |
| “A camera gives better data” | Cameras fail in darkness without infrared and create privacy risk | Use radar where privacy matters |
Signal quality depends mostly on geometry. For a sleep monitoring radar:
A simple test: confirm that the breathing waveform is visible in the app. If the waveform is flat or missing, the radar is not aimed at the chest correctly.
Millimeter wave radar uses FMCW to transmit a sweeping 60 GHz signal, mixes the echo with the transmitted signal to obtain range, and uses FFT and phase analysis to extract micro-movement. At a wavelength of about 5 mm, it resolves chest displacement below 1 mm, which makes breathing rate, heart rate, and sleep stages measurable without contact.
Keep three points in mind: use the 60 GHz band for breathing and sleep, keep the radar within 1.5 m for breathing detection and 2.5 m for sleep and presence detection, and keep fans, air conditioners, moving curtains, and metal out of the beam.
A radar that is correctly aimed produces stable data. If the numbers look unstable, check the installation position and angle first.
tags: mmwave radar - fmcw - 60ghz - breathing detection - presence detection - privacy