Thermapen
Unfold, stick in, see the temperature.
If it's dark, it will highlight the screen, If it's upside down, it will flip the screen.
Very fast, because it uses gradient descend and not linear estimation.
Pull it out, place it down and it switches off. Move it, it switches on.
Single moving part, no buttons. You want it in Farneheights - open it up with a screwdriver, flip a microswitch.
Fairly big in size for no other reason but to be convenient to hold and to read.
Battery last for ages.
And on top of all that it is also very well made.