What it is

It is the strongest independent signal we use: the device itself reports that mains power is present. The request is so simple that it can come from a router, a single-board computer, a $3 board or Home Assistant.

It improves accuracy only when many neighbours do it. One sensor changes nothing publicly: signals appear only when at least five independent sources of the same queue send them, and with a delay.

Privacy

Individual sensors are never shown: not on the map, not in the API. Only aggregates of five or more sensors of the same queue are public, with a delay of at least 30 minutes.
A sensor is tied to a queue, not to an address. We do not ask for an address, name, phone or location.
The ping URL contains a secret token: it is the sensor’s password. Do not publish it in repositories or screenshots. If it leaked, delete the sensor below and create a new one.
Sensor readings are deleted automatically after 48 hours. More: privacy.

Create a sensor

Set up a device

Pick a method. Each one uses the ping URL: before you create a sensor it contains YOUR_TOKEN and after creation it becomes your token.

Connect to the router over SSH and install curl with HTTPS support (on OpenWrt these are the packages curl, ca-bundle).
Add a cron job and start cron.

OpenWrt · SSH

opkg update && opkg install curl ca-bundle
echo '__CRON__ curl -fsS -m 10 "https://svitlopulse.andrewboyko.name/api/v1/sensor/YOUR_TOKEN/ping" >/dev/null 2>&1' >> /etc/crontabs/root
/etc/init.d/cron enable
/etc/init.d/cron restart

The router must have no backup power, otherwise it “sees” power that is already gone. If curl does not fit in flash, uclient-fetch (with libustream-mbedtls) works instead.

Works on a Raspberry Pi, mini PC, NAS and any Linux. Run crontab -e and add the line:

crontab

__CRON__ curl -fsS -m 10 "https://svitlopulse.andrewboyko.name/api/v1/sensor/YOUR_TOKEN/ping" >/dev/null 2>&1

If the device is on a UPS or a battery-backed supply it keeps pinging during an outage. A plain mains socket is what a sensor needs.

A sketch for Arduino IDE or PlatformIO. Works on ESP32 and ESP8266, keeps the Wi-Fi connection and sends a request once per interval.

Arduino · ESP32 / ESP8266

#if defined(ESP8266)
  #include <ESP8266WiFi.h>
  #include <ESP8266HTTPClient.h>
  #include <WiFiClientSecureBearSSL.h>
#else
  #include <WiFi.h>
  #include <HTTPClient.h>
  #include <WiFiClientSecure.h>
#endif

const char* WIFI_SSID = "YOUR_WIFI";
const char* WIFI_PASS = "YOUR_PASSWORD";
const char* PING_URL  = "https://svitlopulse.andrewboyko.name/api/v1/sensor/YOUR_TOKEN/ping";
const unsigned long EVERY_MS = __MS__UL;

void setup() {
  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASS);
}

void loop() {
  if (WiFi.status() == WL_CONNECTED) {
#if defined(ESP8266)
    BearSSL::WiFiClientSecure client;
#else
    WiFiClientSecure client;
#endif
    client.setInsecure();  // simplest; for production pin the root CA with setCACert()
    HTTPClient http;
    if (http.begin(client, PING_URL)) {
      http.setTimeout(8000);
      http.GET();          // 204 = accepted
      http.end();
    }
  }
  delay(EVERY_MS);
}

Power the board from an ordinary USB adapter in a mains socket, not from a power bank. setInsecure() does not verify the server certificate; pin the root certificate for robustness.

Add a command and an automation (Home Assistant 2024.10 and newer syntax):

configuration.yaml

rest_command:
  svitlopulse_ping:
    url: "https://svitlopulse.andrewboyko.name/api/v1/sensor/YOUR_TOKEN/ping"
    method: get
    timeout: 10

automation:
  - alias: "SvitloPulse: датчик світла"
    triggers:
      - trigger: time_pattern
        minutes: "__HAMIN__"
    actions:
      - action: rest_command.svitlopulse_ping

A Home Assistant on a NAS or mini PC behind a UPS “sees” power even during an outage. That is not a sensor but a false “power on” signal.

You can check that the sensor works with one command. The server answers 204 with no body. Both GET and POST are accepted.

curl

curl -fsS -m 10 -o /dev/null -w "%{http_code}\n" "https://svitlopulse.andrewboyko.name/api/v1/sensor/YOUR_TOKEN/ping"
# 204 = accepted

# the same with POST
curl -fsS -m 10 -X POST -o /dev/null -w "%{http_code}\n" "https://svitlopulse.andrewboyko.name/api/v1/sensor/YOUR_TOKEN/ping"

Delete a sensor

Honest about accuracy

Missing pings do not always mean no power: the network, Wi-Fi, the ISP or the device itself may have failed. That is why one sensor decides nothing, and several neighbouring sensors agreeing does.
Backup power (UPS, inverter, power bank, generator) gives a false “power on”. Plug the sensor into a socket without backup.
The signal only adjusts the estimate based on the operator’s schedule, and its influence is capped. See “How it works”.
Do not connect other people’s devices or create several sensors for one home: it adds no accuracy and only distorts the picture.

Home power sensor

What it is

Privacy

Create a sensor

Save the token now

Set up a device

Delete a sensor

Honest about accuracy