You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
I have a surround sound amp for the TV. It now has a powered sub and a Google Chromecast which I would like to only be powered up when the amp. Is on. Is there any kind of current sensing 4 block socket that would switch 1 or several sockets based on the current going up from standby on the main item.
Have a look for ‘Intelliplug’
e.g. https://www.amazon.co.uk/Click-TVA106-Visual-Outlet-Intelliplug/dp/B0026IAXLU
If the amp has a USB port just plug the Chromecast into it. It should also have a 12V connector for triggering other devices.
I'd leave the Chromecast permanently on anyway, that's how they're designed to work.