Re: Weight limit
The exact figure for the weight limit should be determined based on how much weight of explosive would be required to cause real damage.
That is 20-50g of high explosive. Well within what you can pack into any laptop or tablet, even the thinnest one.
The reason for the panic is elsewhere. If the explosive is INSIDE, you can conceal (and even integrate) the wiring needed to detonate it. Security crews are trained to recognize a standalone detonator. They will fail to recognize one inside a computer hooked up to what is supposed to be a battery - it will just look normal wiring to them.