Best answer by Mw2870
If it's the old IHD, the back light should turn off after a few minutes. If you've got a green light on at the top, this might be an alarm to do with your usage targets. You can adjust these yourself: https://www.ovoenergy.com/ovo-answers/topics/smart-technology/smart-meters/how-can-my-ihd-and-smart-meter-help-me-manage-my-energy-use.html.
There's also an off button on the left hand side of the device, which will turn the device off when it's powered by batteries.