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Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →You can use Wi-Fi to monitor sensor data in two different ways: send readings from a conventional sensor over a Wi-Fi network, or analyze changes in the Wi-Fi signal itself. The second approach is called Wi-Fi sensing; a documented way to prototype it is to capture channel state information (CSI) with compatible ESP32 hardware.
CSI is not a ready-made reading such as “person present” or “temperature.” It is radio-channel data that software must process for a specific task. If you need measured temperature, humidity, or another physical value, use an appropriate sensor and transmit its readings over Wi-Fi instead.
How can I use Wi-Fi to monitor sensor data?
First decide whether Wi-Fi is the network carrying sensor readings or the signal being measured. For ordinary monitoring, a sensor measures a physical quantity and sends its reading over Wi-Fi to a receiver or application. For Wi-Fi sensing, a receiver analyzes changes in radio propagation—often caused by movement in the space—to infer a target event.
This article focuses on the second meaning, because it is the less familiar one. Espressif’s ESP-CSI documentation describes a practical prototyping route using ESP32 devices. The method can support experiments such as presence or activity detection, but it requires compatible hardware, captured data, and task-specific software.
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What does Wi-Fi CSI measure?
Channel state information describes characteristics of the wireless channel between a transmitter and receiver. In Espressif’s documented implementation, a receiver estimates channel frequency responses across Wi-Fi subcarriers when packets arrive. CSI samples contain complex values represented by real and imaginary components. The API also exposes reception metadata such as RSSI, RF noise floor, reception time, and antenna information.
Those measurements are not interpretations. A CSI capture does not label a packet “someone entered the room,” identify a person, or report a breathing rate. A sensing application has to filter or transform the measurements and apply an algorithm trained or designed for its particular task.
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Which ESP32 setup should you use?
Espressif’s ESP-CSI guide describes three collection arrangements. The right choice depends on whether you want a quick prototype using an existing router or a setup with more control over packet transmission and receiver placement.
| Arrangement | Hardware described | Router dependence | Trade-off |
|---|---|---|---|
| Router as transmitter | One ESP32 and a Wi-Fi router | Depends on router location and supported Wi-Fi protocol | Uses fewer dedicated boards; the router’s position and compatibility affect collection. |
| ESP32-to-ESP32 | Two or more ESP32 boards exchanging traffic | Less dependent on router placement | Provides a more controlled transmitter–receiver arrangement, but still depends on protocol support and the environment. |
| Dedicated packet sender with multiple receivers | A packet-sending device and multiple ESP32 receivers | Less dependent on a router | Requires additional sender hardware. Espressif describes it as the most accurate and reliable of these example arrangements; that is implementation guidance, not an independent benchmark. |
Before choosing a board, verify CSI support for the particular chip and the ESP-IDF release you plan to use. Espressif maintains an ESP-CSI guide with sender, receiver, router-based collection, analysis, and human-activity-detection examples. A separate esp_wifi_sensing component registry entry lists ESP-IDF 5.4 or later as a dependency. The cited ESP-IDF driver reference is for release 5.1, so do not assume its API details apply unchanged to every newer chip or release.
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How do you start collecting CSI?
At a high level, an ESP-IDF capture follows this sequence:
- Enable CSI in the project configuration for the selected target and SDK.
- Register a callback to receive CSI data when packets arrive.
- Set the CSI configuration appropriate to the capture.
- Enable CSI and collect packets from the chosen transmitter arrangement.
The data layout depends on the Wi-Fi protocol and channel width. For example, Espressif’s ESP32 documentation lists 52 total and 48 usable subcarriers for 802.11a/g; 56 total and 52 usable for 802.11n at 20 MHz; and 114 total and 108 usable for 802.11n at 40 MHz. These figures describe the documented ESP32 PHY modes, not every Wi-Fi receiver or Wi-Fi generation. Espressif also warns that, in some cases, an initial word in the capture can be invalid because of an ESP32 hardware limitation.
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Capturing CSI is only the data-collection stage. To monitor a real event, you still need software that turns the stream into a task-specific result, such as a motion classification. Espressif’s examples include analysis scripts and human activity detection, but an example is not a guarantee that the same model will work in a different room or with different hardware.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What affects results in a room?
There is no generally applicable detection range or accuracy figure established for the setups described here. Room layout, receiver and router positions, antenna orientation, packet traffic, and movement during calibration can all affect the radio measurements. Espressif advises testing in an unoccupied environment and avoiding other people’s activity during tests. Its ESP-CSI guide also says external IPEX antennas can perform better than PCB antennas and notes that PCB antennas have directionality.
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Controlled research illustrates why performance claims should stay tied to the conditions tested. A 2023 study by Marco Cominelli, Francesco Gringoli, and Francesco Restuccia collected 80 GB of Wi-Fi 6 CSI data from three people, in three environments, performing twelve activities; video provided anonymized ground truth. The authors reported that MIMO and higher spectral resolution might benefit sensing more than simply increasing bandwidth, and that environment-independent sensing remained uncertain. This study is evidence about its particular dataset and settings, not a universal consumer-device test.
- Start with the event you want to detect; different tasks require different interpretation algorithms.
- Keep transmitter and receiver placement stable while collecting a baseline and testing.
- Record the hardware, protocol, antenna orientation, room conditions, and software version alongside captures so results can be interpreted in context.
- Test under the conditions where the system will actually be used rather than treating one successful demonstration as proof of general performance.
Is Wi-Fi sensing standardized?
Existing Wi-Fi standards can support some sensing applications, but that does not mean sensing works interoperably across all routers and receivers. The Wireless Broadband Alliance’s page titled “2024 Edition” says technology gaps limit the range of applications and identifies IEEE task group 802.11bf as work on sensing-specific improvements. The page metadata displays “WBA white papers; April 2021,” so its displayed title should not be treated as confirmation of a precise publication date or of the current status or deployment of an 802.11bf amendment.
For a prototype, check the supported chip, protocol, SDK, and example together. For a deployment that must work across devices or locations, do not assume that a standard or a successful ESP32 experiment alone establishes compatibility or performance.
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