I was just thinking if it is possible to use a USB charger as some kind of monitoring or surveillance if the attached device was taken (unplugged). Is there something like this?
Attaching a typical smart plug before the charger won’t help, as it probably can’t tell the difference if a usb device is plugged and not charging, or not plugged at all.
I suppose the USB controller in a modern USB-C charger has that information, but that migth depend on the supported charging types? Not sure.
You need an USB charger that are connected to HA in some way.
Most USB chargers have no connectivity options.
Sonoff has one though: SONOFF Micro USB Smart Adaptor - remotely control USB Devices
This might be able to tell you that a device is drawing power, but some devices, like modern phones will have a battery charge controller, that will disconnect the charger after a pattern and then it might look like the device is not connected anymore.
I have my Quest 2 connected to a USB charger plugged into a power monitoring switch. It only draws power about once a week when the battery drains to a certain level, and only for an hour. I doubt there’d be a device that knows if something is physically plugged in but not drawing power. So it would only work if it’s a device that does not have a battery and constantly draws power.
If it’s never supposed to move, you could just stick a motion sensor on the actual device. Otherwise you could perhaps put an iBeacon on it, and detect when it leaves the house.
If the device you want to monitor has any ‘smarts’, it might present some state or signal on the data lines of USB. It would require some kind of DIY ESP (or similar) device inserted after (or replacing) the wall wart. Good hunting!