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Sign-off (or closedown) is the sequence of operations involved when a radio or television station shuts down its transmitters and goes off the air for a predetermined period; generally this occurs during the overnight hours. It is the opposite to a sign-on (or startup) which usually takes place at the start of the day.
Sign-offs, like sign-ons, vary from country to country, from station to station, and from time to time, however most follow a similar general pattern. Many stations follow the reverse process to their sign-on sequence at the start of the day. Sign-off messages can be initiated by a broadcast automation system just as for other television programming, and automatic transmission systems can cutoff the carrier signal and trigger the actual shutdown of the transmitter by remote control. Generally, after the carrier signal is cut, the viewer only sees or hears static.
Both sign-offs and sign-ons have become less common with the increasing prevalence of twenty-four hour a day, seven day a week broadcasting. They are, however, still conducted by a number of stations around the world, often by stations catering to small-markets or those in less developed countries, or when stations need to shut down for transmitter maintenance. Another consideration for whether providers shutdown is power consumption; aerial signals, such as those for UHF analog TV transmissions, can require tens of thousands of watts of power, making electricity a major expense, while power consumption would usually be considerably lower for cable and satellite providers. Third, in relation to costs, viewer numbers are also a consideration. A fourth consideration is the licence issued by the government which indicates when their transmitters can be operated.
For broadcasters that do still close for a period each day, the station close most often takes place overnight or during the early hours of the morning. The daily sign-off typically occurs between around 11:00 pm and 2:00 am, and the station will remain closed until about 5:00 am to 7:00 am, although in countries with limited broadcast coverage, sign-off may occur at earlier times, and sign-on later. Sign-off may also vary depending on the day of the week, for example some broadcasters may run for 24 hours on Saturday nights, but sign-off and close during the week when there are lower viewer numbers. Seasonality is also a consideration where some stations/networks stay open for 24-hours, while rarely few go off the air completely during peak times of religious observances.
Many stations, while no longer conducting a sign-off and being off air for a period of time each day, instead run low quality, low cost programming during those times of low viewer numbers. This may include paid programming such as infomercials, old movies, television, or radio shows, simple weather forecasts or information services, often backed by public domain music or local radio stations, low cost news or infotainment programming from other suppliers, replays of earlier programming, or feeds of local cable TV companies' programming via a fiber optic line to the cable headend. Other broadcasters that are part of a radio or television network may run an unedited feed of the network's overnight programming from a central location, without local advertising. Some stations, after doing a sign-off, nonetheless continue to transmit throughout the off-air period on cable/satellite; this transmission may involve a test pattern, a static image, or text based news items, often with backing music.
Sign-off sequence 
The sign-off sequence may include some or all of the following stages, but not necessarily in this order:
- An announcement made about the upcoming sign-off to inform the viewers that the station is about to go off-air.
- A station jingle or slogan may be played, accompanied on television with video clips featuring station programming or personalities. A series of program trailers may also be played.
- A prayer, hymn, or other religious acknowledgement, particularly in countries with a state religion, in theocracies, and on religious broadcasters. For example, closedowns in Malaysia, Saudi Arabia, Morocco and the United Arab Emirates generally include a fifteen-minute reading from the Qur'an and a call for the midnight salah; stations in Macau, Thailand, Sri Lanka and Hong Kong typically have a quote from Buddha, stations in Israel follows a Jewish prayer; while many stations in the Philippines, Vietnam, Lebanon, South Korea and in the Southern United States include a Christian prayer or hymn of some type.
- A short weather forecast, newscast, or a pre-taped inspirational message known as a sermonette.
- A "goodnight" message to viewers or listeners thanking them for their patronage, along with an announcement of the time when the station is scheduled to sign on again.
- A program guide for the following day's programs.
- Ownership information about the station and a list of related organizations.
- Contact information, such as street and mailing addresses, telephone number, email, and website details.
- Technical information provided, such as the call sign, transmitter power, translators used, transmitter locations, a list of engineers, and studio/transmitter links (STL).
- A disclaimer that station programming is taped, aired live, or originates from a television or radio network.
- Another disclaimer that programs are for personal use only (sometimes with information on copyright restrictions), and a statement that businesses cannot profit from showing them by applying a cover charge for viewing.
- A statement of commitment to quality; this may be in the form of a recognized standard, such as the United States National Association of Broadcasters' "Seal of Good Practice".
- An invitation to tune-in to alternate services hosted by their sister/affiliate stations (e.g. radio stations). In the UK for example, when BBC1 or 2 closed down for the day, the announcer invited the outgoing viewers to tune-in to BBC radio services during the TV station's off-hours.
- On television stations, a video and/or photo montage set to the national anthem or another patriotic piece of music may be played; on radio stations, this would just consist of the music, usually the national anthem. The accompanying television video usually involves images of the national flag, head of state, military, national symbols, or other nationalistic imagery, particularly on state owned broadcasters.
- The station may display some type of novelty item, such as an animated character, particular to that station or its locale.
- The display of a test pattern, a variation on the station logo, or a black signal, often accompanied by a monotone sound for a short period of time; radio stations may just play a monotone.
- Viewers may be warned to remember to turn off their television sets just prior to the transmitter being switched off; these announcements were particularly common in the early days of television, but are still in regular practice in some places, such as Russia until the mid nineties.
- A signal to turn off remote transmitters may be played—this is usually a series of touch tones. Once the transmission has been cut off there will usually only be video static on television stations or radio static on radio stations.
- A loud tone may be played on the audio to encourage sleeping viewers to turn their television sets off.
While most of these sign-off steps are done as a service to the public, or for advertising reasons, some of them may be required by the government of the country. For example, in the US or in the Philippines, the Federal Communications Commission (FCC) regulations, or the National Telecommunications Commission require stations to identify themselves before leaving the air, which usually means they must announce their calls, city of license, and broadcast frequency or channel number.
Special cases 
In a number of countries closedowns formerly took place during the daytime as well as overnight. In the United Kingdom this was initially due to Government-imposed restrictions on daytime broadcasting hours, and later, due to budgetary constraints. The eventual relaxation of these rules meant that afternoon closedowns ceased permanently on the ITV network in October 1972, but the BBC maintained the practice until late 1986, before commencing a full daytime service. Afternoon closedowns continued in South Korea until December 2005. Hong Kong's broadcasting networks also practiced this until the early 2000s. In these cases, the station's transmitters later didn't actually shut-down for the afternoon break; either a test-card was played or a static schedule was posted telling viewers of the programming line-up once broadcasting resumes.
During Holy Week in the Philippines (particularly Holy Thursday, Good Friday and Black Saturday), most terrestrial television and radio stations remain off-air for the entire day, and others commence transmission much later in the morning or at midday. During Ramadan, Malaysian public broadcaster RTM operates TV1 24 hours a day instead of signing off, but this would be its last as TV1 becomes 24 hours to coincide with their sister channel, TV2 by showing reruns of their old programmes shown on this broadcaster and telemovies on early-mornings before start-up.
See also 
- Goodnight Kiwi
- ITV Nightscreen
- Dark (broadcasting)
- DTV transition in the United States
- Short-term Analog Flash and Emergency Readiness Act