Monostable multivibrators or one-shots are digital logic devices that have only one stable state. By contrast, flip-flops and latches are bistable devices that can remain in either a set or reset state for an indefinite period of time. Monostable multivibrators remain in their stable state indefinitely, until an external input is applied. Once triggered, the output is temporarily switched to another state. Because they are timed devices, monostable multivibrators can hold their unstable output state for only a limited amount of time. With semiconductor monostable circuits, this timing function is often accomplished through the use of resistors and capacitors. In terms of a mechanical analogy, monostable multivibrators are like momentary contact pushbuttons that spring-return to a normal (stable) position when pressure is moved from the button actuator. Conversely, bistable devices such as flip-flops and latches are like standard wall or toggle switches that turn lights either on or off.