electronic Laptop detector

certainly yes.

Its very easy things to detect the electric appliance position when it works.

rf detector can do it.

But the laptop is turned off. rf detector can only detect it is turn on.

Yes. They range the streets of most cities, armed with various mechanical aids for getting the thing open and taking them with impunity. They are called "thieves".

Seriously, there is a glut of laptops in the UK at present, and the retail prices have dropped substantially. Thieves are taking unattended satellite navigation systems instead.

I am told the military has such devices available, but they are not for sale to the public currently.