The Flashlight is a portable light source used throughout the Half-Life series appearing in a variety of shapes and forms. It is standard equipment for the Black Mesa Security Force and a built-in feature of the HEV Suit.
First formally introduced during the Hazard Course training, the flashlight is a tool used to illuminate dark areas, such as through Black Mesa's numerous ventilation ducts. The HEV Suit includes a built-in flashlight that runs on an auxiliary source independent of the suit's power supply, allowing it to be used even if the suit is fully drained. The flashlight slowly drains its energy supply while in use and recharges when turned off. If kept on for too long, the flashlight will automatically shut off once it depletes its available power. Black Mesa security guards carry handheld flashlights that function in the same manner. The science personnel in the facility are also seen wielding a variety of portable light devices. However, the invading HECU and Black Ops forces instead opt for night vision goggles, the former as a part of their Powered Combat Vest outfit.
Half-Life 2: Episode One features a segment in which Gordon and Alyx must travel through pitch-black underground tunnels overrun with Zombies using only his suit's flashlight and flares for illumination. Zombies hidden in darkness are instantly attracted to the light source, and Fast Headcrabs clinging to the ceiling in ambush will immediately strike if a light shines upon them. In Half-Life 2: Episode Two, the flashlight was given a separate power source that had previously been shared with the sprinting and oxygen meters.
In Portal 2, the Aperture Science Personality Constructs are shown to have built-in flashlights projected from their eyes. This is demonstrated by Wheatley in Turret Manufacturing when the power to the wing is shut off. He states that he was told he would die if he were ever to turn his flashlight on.
 Behind the scenes
In the Half-Life Alpha, the HEV Suit's flashlight acts in a different manner. Rather than projecting a point of light, it simply illuminates a limited area around the player, similar to how the night vision functions in Half-Life: Opposing Force. A handheld version of flashlight acting as a unique weapon slot item can be seen in an early Half-Life: Blue Shift trailer. This feature was cut from the final game, instead retaining the same flashlight mechanics used for the HEV Suit in Half-Life. The leftover flashlight worldmodel was kept as a decorative map object.
According to Valve's Aaron Seeler, the reason why the flashlight was given a separate power source in Episode Two is related to the Antlion Guardian chase sequences. Playtesters were unable to outrun the creature because they constantly left their flashlight on while escaping, leaving no energy left to sprint. The development team didn't want to force the players to not illuminate their surroundings, so they decided to alter the mechanic. Seeler notes that this change might be explained in-universe as being the result of damage sustained in the train crash.
HECU Marines shine a spotlight on a Panthereye.
Spotting a Zombine with the HEV Suit's flashlight.
 List of appearances
 Main games
- Half-Life: Blue Shift
- Half-Life: Decay
- Half-Life 2
- Half-Life 2: Deathmatch (Non-canonical appearance)
- Half-Life 2: Episode One
- Half-Life 2: Episode Two
- Portal 2
- Half-Life: Day One (First appearance)
- Half-Life: Uplink (Non-canonical appearance)
- Half-Life 2: Lost Coast (Non-canonical appearance)
- Source Particle Benchmark (Non-canonical appearance)