Therefore in electronic devices where the clock is not a critical function, often they are not set at all, displaying the default after powered on, 00:00 or 12:00.
Since they run on electricity, digital clocks must be reset every time the power is cut off
This is a particular problem with alarm clocks that have no "battery" backup, because even a very brief power outage during the night usually results in the clock failing to trigger the alarm in the morning.
To reduce the problem, many devices designed to operate on household electricity incorporate a battery backup to maintain the time during power outages and during times of disconnection from the power supply
More recently, some devices incorporate a method for automatically setting the time, such as using a broadcast radio time signal from an atomic clock, getting the time from an existing satellite television or computer connection, or by being set at the factory and then maintaining the time from then on with a quartz movement powered by an internal rechargeable battery.
A digital clock built into an oven.
Because digital clocks can be very small and inexpensive devices that enhance the popularity of product designs, they are often incorporated into all kinds of devices such as cars, radios, televisions, microwave ovens, standard ovens, computers and cell phones
Sometimes their usefulness is disputed: a common complaint is that when time has to be set to Daylight Saving Time, many household clocks have to be readjusted
The incorporation of automatic synchronisation by a radio time signal is reducing this problem (see Radio clock).


A human speaking clock prior to the invention of automated equipment
A speaking clock service is a recorded or simulated human voice service, usually accessed by telephone, that gives the correct time.
The format of the service is somewhat similar to those in radio time signal services
Every ten seconds or so, a voice announces "At the third stroke, it will be [for example] twelve forty-six and ten seconds...", with three beeps following
At the third beep, the time at that point is the time announced previously
Some countries have sponsored time announcements and include that in the message.
In Australia, the number 1194 gives the speaking clock in all areas and from all providers
It is always the current time from where the call originates
A male voice says "At the third stroke, it will be (hours) (minutes) and (seconds) seconds/precisely