A time switch is a timer

Timer

A timer is a specialized type of clock. A timer can be used to control the sequence of an event or process. Whereas a stopwatch counts upwards from zero for measuring elapsed time, a timer counts down from a specified time interval, like an hourglass.Timers can be mechanical, electromechanical,...

 that plugs into an electric socket, between the socket itself and a power plug. This physical arrangement allows the connected device(s) to automatically receive power for a desired duration of time. There are also time switches with several power plugs that can be independently programmed to turn on and of at specified times.

Time switches are available in both mechanical

Mechanical engineering

Mechanical engineering is a discipline of engineering that applies the principles of physics and materials science for analysis, design, manufacturing, and maintenance of mechanical systems. It is the branch of engineering that involves the production and usage of heat and mechanical power for the...

 and completely electronic

Electronics

Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

 versions. They are commonly utilized in the following applications: aquariums

Aquarium

An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...

, home lighting

Lighting

Lighting or illumination is the deliberate application of light to achieve some practical or aesthetic effect. Lighting includes the use of both artificial light sources such as lamps and light fixtures, as well as natural illumination by capturing daylight...

 (both interior and exterior), ovens

Oven

An oven is a thermally insulated chamber used for the heating, baking or drying of a substance. It is most commonly used for cooking. Kilns, and furnaces are special-purpose ovens...

, street lights

Street light

A street light, lamppost, street lamp, light standard, or lamp standard is a raised source of light on the edge of a road or walkway, which is turned on or lit at a certain time every night. Modern lamps may also have light-sensitive photocells to turn them on at dusk, off at dawn, or activate...

 and washing machines

Washing machine

A washing machine is a machine designed to wash laundry, such as clothing, towels and sheets...

. In cold climates, block heater

Block heater

A block heater warms an engine to ease and speed starting and vehicle warmup in cold weather. The most common type is an electric heating element connected through a power cord often routed through the vehicle's grille. The block heater may replace one of the engine's core plugs, or may be...

s, battery blanket

Car battery

An automotive battery is a type of rechargeable battery that supplies electric energy to an automobile. Usually this refers to an SLI battery to power the starter motor, the lights, and the ignition system of a vehicle’s engine...

s and interior car warmers may be plugged into a timer that switches them on an hour or two before planned use of the vehicle, saving energy; outdoor weather-resistant timers are sold for this purpose.

Permanently-installed ("hard-wired") time switches may be installed to control exterior lighting of buildings. "Astronomical" time switches are constructed to compensate for the varying length of day, so that lighting turns on at dusk and off at dawn.