Introduced in 1940, power windows have become a common feature in many modern cars, trucks, and SUVs. Unlike older window systems which require occupants to manually turn a crank to raise or lower windows, power windows are controlled with the simple push of a button or flip of a switch. Because power windows rely on electricity to work, most are inoperable once a vehicle stops running. However, some power windows feature a time delay that allows drivers and passengers to continue operating the windows for a short amount of time after the engine stops. Because power windows are easy to trigger, most vehicles also feature a safety lock that drivers can use to prevent other passengers, such as small children, from erroneously opening or closing the windows. Overall, power windows are a convenient feature that many motorists enjoy.