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+## OTA Updates
+
+From [firmware version 3.1.1](https://github.com/airgradienthq/arduino/tree/3.1.1) onwards, the AirGradient ONE and Open Air monitors support over the air (OTA) updates. 
+
+#### Mechanism
+
+Upon compilation of an official release the git tag (GIT_VERSION) is compiled into the binary.
+
+The device attempts to update to the latest version on startup and in regular intervals using URL
+
+http://hw.airgradient.com/sensors/{deviceId}/generic/os/firmware.bin?current_firmware={GIT_VERSION}
+
+If does pass the version it is currently running on along to the server through URL parameter 'current_firmware'. 
+This allows the server to identify if the device is already running on the latest version or should update.
+
+The following scenarios are possible
+
+1. The device is already on the latest firmware. Then the server returns a 304 with a short explanation text in the body saying this.
+2. The device reports a firmware unknown to the server. A 400 with an empty payload is returned in this case and the update is not performed. This case is relevant for local changes. The GIT_VERSION then defaults to "snapshot" which is unknown to the server.
+3. There is an update available. A 200 along with the binary data of the new version is returned and the update is performed.
+
+More information about the implementation details are available here: https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/system/ota.html