Daylight Saving Time is often referred to as "Summer Time", "DST" or "Daylight Savings Time". DST begins on the second Sunday in March and ends on the first Sunday in November.
Benjamin Franklin first suggested Daylight Saving Time in 1784, but modern DST was not established in U.S. law until the Act of March 19, 1918, sometimes called the Standard Time Act. The act also established daylight saving time, a contentious idea then. Daylight saving time was repealed in 1919, but standard time in time zones remained in law.
Daylight time became a local matter. It was re-established nationally early in World War II, and was continuously observed from 9 February 1942 to 30 September 1945. After the war its use varied among states and localities. The Uniform Time Act of 1966 provided standardization in the dates of beginning and end of daylight time in the U.S. but allowed for local exemptions from its observance. The act provided that daylight time begin on the last Sunday in April and end on the last Sunday in October, with the changeover to occur at 2 a.m. local time.
During the "energy crisis" years, Congress enacted earlier starting dates for daylight time. In 1974, daylight time began on 6 January and in 1975 it began on 23 February. After those two years the starting date reverted to the last Sunday in April. In 1986, a law was passed that shifted the starting date of daylight time to the first Sunday in April, beginning in 1987. The ending date of daylight time was not subject to such changes, and remained the last Sunday in October. The Energy Policy Act of 2005 changed both the starting and ending dates. Beginning in 2007, daylight time starts on the second Sunday in March and ends on the first Sunday in November.**
In the U.S., daylight saving time is not observed in Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands and the state of Arizona (with the exception of the Navajo Indian Reservation, which does observe DST).
The time change is also used as a good reminder from fire prevention organizations. When you turn the clocks ahead, take a few minutes to replace the batteries in your smoke alarms and push the test button to make sure the alarms are working. It's also a great time to check your carbon monoxide detectors.
(**information in italics provided by answers.usa.gov)
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