The "pump handle" detonators have a generator geared to the rod that the handle sticks out of. When you push the plunger down it spins up the generator and then closes a contact when it hits the bottom, firing the det charges.
If you make your plunger stiff enough (oo-er) then it won't drop down on its own (oo-er). If you use a motor as a generator you could try shorting across its terminals - this is how electromagnetic brakes on vehicles (retarders) work.