Twilight Sentinel is a system in General Motors cars that uses a photoelectric cell in the dashboard to sense outside light and darkness and turn the exterior lights off and on accordingly. The Sentinel also includes a timer, which can be used to keep the headlights on after the key is removed from the ignition switch, usually up to three minutes.

The sensor system turns the lights on or off once a change in ambient light has lasted about 10 seconds.

Twilight Sentinel can be turned off. It also can be bypassed by manually turning on the headlights. Older versions did not turn on the exterior lights for daytime driving conditions such as fog and heavy rain; improvements linked the Sentinel to RainSense, GM's automatic windshield-wiper system, to turn lights on automatically when the wipers are on.

Twilight Sentinel was first offered on the 1964 Cadillac lineup and was later expanded to other GM makes.

A related feature offered on many General Motors models in the 1950s and 1960s was the Autronic Eye headlight dimmer. Cadillac later named the system "Guidematic Headlamp Control", which encompassed Twilight Sentinel and Dimming Sentinel controls.

Ford Motor Company offers a nearly identical exterior lights on/off/delay shut-off system, called "AutoLamp". The Ford system could be had with automatic dimming on Lincoln models. Chrysler offered Twilight Sentinel on the Imperial from 1967 to 1975; other full-size C-body Chrysler products from the mid-sixties to the mid-seventies also had it as an option.^{[citation needed]}