Kill A Watt

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This Kill A Watt model P4400 is displaying a current draw of 10.27 amp in this mode.
Prodigit Model 2000MU (UK version), shown in use and displaying a reading of 10 Watts being consumed by the appliance

The Kill A Watt is an electricity usage monitor marketed by P3 International. It features a large LCD display and it enables cost forecasting.[1] It measures the energy used by individual appliances plugged into the meter, as opposed to in-home energy use displays, which display the energy used by an entire household. The name is a play on the word kilowatt.

Having a NEMA 5-15 plug and receptacle, and rated for 120 VAC, the Kill A Watt is sold for the North American market. The manufacturer is the Taiwanese company Prodigit,[2] which also makes models suited for 240 V with European Schuko, U.K. BS 1363 and Australian AS 3112 receptacles as well as a model compatible with 100 VAC for the Japanese market (2022-04,[3] marketed there as the Watt Checker [ワットチェッカー] Plus by other companies).

The device can give an indication of the standby power used by appliances.[4]


There are several different models of Kill A Watt meters:


This is the original, most basic version, based on the Prodigit 2000M.[5] From the time it is plugged in, it measures:

The power and kilowatt-hour settings are the most widely used, to measure how much power devices use, and how much total energy they use over time. When electricity is disconnected, the P4400's measurements and meters are reset.[6]

P4460 Kill A Watt EZ[edit]

This is an enhanced version, based on the Prodigit 2022,[7] which includes a backup battery to preserve measurements when disconnected from electricity. It has the same capabilities as the P4400, and can be programmed with electricity cost information, which enables it to display the cost of the electricity consumed to date. From this, it can calculate cost per hour, day, week, month, or year.[8]

P4320 Kill A Watt PS[edit]

This model, based on the Prodigit 2024,[9] is integrated into an eight-outlet power strip. Unlike the other models, it does not display frequency or apparent power. It protects against surges and EMI, has a configurable overcurrent shutdown limit, and also measures earth leakage current; one version acts as an earth leakage circuit breaker (ELCB).[10] It switches power on or off at an AC zero crossing, minimizing current surges and interference.[11]

Open-source modifications[edit]

One shortcoming of the Kill-a-Watt range of devices is that they do not have the ability to store, transmit or transfer the readings, thus limiting their usage for any ongoing monitoring purposes. To counter this shortcoming, a couple of openly available modifications have been published on the Web, to enable these devices send data wirelessly to a receiver.


The Tweet-a-watt[12] is a hacked version of the standard Kill-A-Watt Plug in Power Meter. By piggybacking on the devices on-board LM2902N op-amp chip, the creator was able to get readings for voltage and current and transmit to a computer, which then sent this to Twitter via handle @tweetawatt.[13] At the time it gained quite a lot of interest on the Web, but interest waned after some time. The last tweet from this handle was in March 2010.


Following the usefulness of the Tweet-a-Watt, designs for the MoteWatt were released on the Web by another hobbyist, Felix Rusu at LowPowerLab.[14] These new designs featured much cheaper enhancements and required less solder work. The modifications using a customized clone of the Arduino chip known as the Moteino, this version was much cheaper and required much less soldering than the original design. Further optimizations on the design were done by Mike Tranchemontage,[15] his designs featured a more robust power supply unit to the moteino chip, avoid problems capacitors which discharged too slowly with the original design.

See also[edit]


  1. ^ Edwin Kee (2008-05-26). "Cost-saving and handy devices". New Straits Times. 
  2. ^
  3. ^ Model 2022-04 Manufacturer's web site.
  4. ^ "Gadgets that help save energy". Bloomberg News. 2008-05-04. pp. F02. 
  5. ^ "Prodigit 2000M 8-in-1 Plug-in Power Monitor". Retrieved 2009-07-16. 
  6. ^ P4400 Kill A Watt Manufacturer's web site.
  7. ^ "Prodigit 2022 Energy Cost Monitor". Retrieved 2009-07-16. 
  8. ^ P4460 Kill A Watt EZ Manufacturer's web site.
  9. ^ "Prodigit 2024 8 Port Power Safer". Retrieved 2009-07-16. 
  10. ^ P4320 Kill A Watt PS Manufacturer's web site.
  11. ^ Power Safer — New Safety Revolution For Power Strip Fairly thick chinglish, but informative technical description of the features provided.
  12. ^ Retrieved 1 November 2013.  Missing or empty |title= (help)
  13. ^ Retrieved 1 November 2013.  Missing or empty |title= (help)
  14. ^ Rusu, Felix. "Meet the WattMote (Moteino based Tweet-A-Watt)". Retrieved 12 December 2013. 
  15. ^ Tranchemontagne, Mike. "Moteino Kill-A-Watt: Hardware". Retrieved 12 December 2013. 

External links[edit]