Versatile, affordable electrical energy monitoring.

IoTaWatt is a Work-in-Progress. The hardware is a simple ESP8266 WiFi IoT device that was created to run the free open software. The hardware will be available soon through this site for North American users as regulatory and safety certifications are completed. We will also offer a selection of UL approved current sensors and power supplies. It is currently CE compliant and available through the Open Energy Monitor store in the UK. Hundreds have been sold and are operating in Europe, Australia, and North America.

Support is via the IoTaWatt Discourse forum.

Source code and hardware design are available in the IoTaWatt Github Repository.

Documentation is currently available in the Github Wiki, but will soon migrate to a Read-the-Docs site.

IoTaWatt is an open source/open hardware electric power monitor capable of measuring Volts, Amps, Watts, kWh, VA, power-factor, and frequency for up to 14 circuits.

It is classified as a low-voltage device and is powered by a USB plug. Passive current transformers are placed around a conductor of each circuit to be measured. There is no contact between the sensor and the live wire. It senses the magnetic field generated by current flowing through the wire to accurately measure the power used by the circuit.

During installation, the configuration app is used to specify what's connected using the browser on your computer, smartphone or tablet. Everything is intuitive and menu driven.




Each circuit is labelled and the type of CT used is selected from an extensive dropdown menu of supported models.



The current status of all inputs can be continuously displayed in a browser window. User specified outputs are displayed alongside the basic input data.

There are also various dropdown tabs to activate status display of the basic device status, cloud server upload, and data logging history.

Integrated analytic tools allow viewing usage graphically. Show total power use along with individual circuits by simply selecting from a menu.

More sophisticated users can configure data upload to influxDB and use Grafana or one of several other visualization tools to create stunning dashboards.

There is also an option to upload to the Emoncms system with it's own integrated graphical tools.

Both of these external data bases are open software and available as commercial services or hosted on various personal platforms including windows and RaspberryPi.

The "calculator" is IoTaWatt's simple interface for creating scripts to combine and export data. You specify the units to calculate (Amps, Watts, Volts etc.) and then enter the function to calculate the value. It's as easy as using a basic four-function calculator.

There's a lot going on with this project, and these are a few of the additional capabilities and features:


There has been no independent testing of the accuracy of IoTaWatt. There is an ongoing comparison of an IoTaWatt installation and several 1% revenue grade meters. IoTaWatt has been tracking these "standards" to less than 0.5% deviation for the past six months measuring whole house, as well as mostly unity power factor and more reactive loads. The device has a built-in calibration reference and provision for easy micro-calibration of line voltage sense using the browser based configuration utility. Most installations just use it right out of the box. There have been numerous user reports of similar results in both single phase and three-phase installations.

Integrated WiFi

IoTaWatt connectes to the internet using your WiFi network.

Automatic Software Upgrade

New releases of the firmware and related apps are available from the site. You can configure your IoTaWatt to automatically download and install new releases depending on your preference for the latest ALPHA software of the tried and true MAJOR releases, and a few choices in-between. You can also opt-out of automatic updates. Updates are digitally signed, so new releases are verified authentic before they are installed.

Three-Phase power

While most US residential power is 120/240 single-phase, three-phase power is common in many commercial buildings. IoTaWatt can be used to measure three-phase power using two different methods.

Internet Security

Newer releases of the firmware support password authorization for access on two levels - essentially administrative and read-only user. While not capable of supporting the most advanced encryption protocols, the cryptographic digest method of authentication used can provide security appropriate for the exposure. With secure passords specified, it's possible to configure wider internet access using port forwarding or VPN connection through your router.

There is also a secure encrypted protocol that can be used to send data to Emoncms over the internet.

Local Datalog

There is an 8Gb SD card inside that can hold decades of historic data. IoTaWatt keeps all of the most current year's worth of data at 5 second resolution for analysis or download. The associated history log keeps the same data at one minute resolution for up to fifteen years. All of the data, whether in the current or history log, is avilable through the web server APIs for retrieval.

Robust Server Upload

When configuring to upload to one or more servers, you specify the related account information, web address, interval that you want to upload (5, 10, 15... seconds) and the data that you want to send. IoTaWatt will send the data as collected. In the event of a lapse in communication or other problem accessing the remote server, IoTaWatt will continue to accumulate data, as it always does, on the local SD card. When service is restored, whether in minutes, hours, or weeks, IoTaWatt will bulk upload all of the backlog data seamlessly.

Enterprise Ready

All of the pieces are in place to deploy many individual IoTaWatt devices to monitor energy across multiple buildings, campuses, or even offices in different countries. The influDB upload capability can post data from many units to a large single database with unique keys to identify each installation. The data can be monitored, aggregated, and analysed using any number of tools that are adapted to use the SQL like influxQuery.