Early devices were based on an electromechanical system identical to an electric bell without the metal gong.
From the en.wikipedia.org
In an electric bell-style alarm clock, the bell is rung by an electromagneticcircuit and armature that turns the circuit on and off repeatedly.
From the en.wikipedia.org
In the summer of 1894, he built a storm alarm made up of a battery, a coherer, and an electric bell, which went off if there was lightning.
From the en.wikipedia.org
Untitled by Maurizio Cattelan, a 2001 mini-elevator made of stainless steel, composition wood, electric motor, electric light, electric bell and a computer.
From the ocregister.com
If, after the conditioning, the bell rings but the electric shock fails to follow, the rats will gradually learn that the connection no longer obtains.
From the economist.com
At electric instruments this technique can generate multitone sounds remniscent of a clock or a bell.
From the en.wikipedia.org
And on stage this night there was a violinist and upright electric bass and trombone along with that beautiful bell tones of the Fender Rhodes piano and more.
From the npr.org
However, his writings record the use of a wide variety of stimuli, including electric shocks, whistles, metronomes, tuning forks, and a range of visual stimuli, in addition to ringing a bell.