No

Thanks for the info, only just realised it doesn't have a clock and date display, so it's not what I'm looking for anyway.

No, you can actually only switch from °F to °C on the device. But as Tabbit96 already wrote, this makes no sense and if you don't connect anything to it, it is a normal thermo/hygrometer.

I don't think so, why do you want to switch it off? Doesn't make sense, then you can just use a normal thermo/hygrometer.