In Destroy all humans path of the furon, there are four alert levels, each with their own color-coded meters.
There are multiple ways to lose alert including body snatch, saucer cloak, enter/exit challenge or by dying and respawning at the nearest landing zone.
The meters are as follows:
- Green= police.
- yellow= SWAT.
- orange= military.
- Red= nexos.
Depending on the situation, there will be on-screen messages like "alert up", "alert down" and "all clear", with the last of the three being displayed if the player dies.
Green: 2 or 3 police cars are sent after the player, with each containing one officer per car. If players kill the cops, police radio will call for backup, which consists of 3-4 cars and 2 officers per car. Also, 2 foot cops will appear on foot. All police carry pistols.
Yellow: The SWAT show up in SWAT vans, which can occupy 5 members. SWAT carry pistols and shotguns, but some carry riot shields to block players attacks. In addition, 2 SWAT also spawn on foot.
Orange: The military dispatch tanks, drop-ship choppers, attack choppers, rocket trucks and soldiers to kill the player. After some time, Military backup will be called in, which consists of even more tanks, choppers and artillery trucks deployed. The soldiers carry assault rifles, whilst all military vehicles use some form of homing rocket against crypto and the saucer.
Red: the final alert level. Here nexo aliens teleport into the map, destroying and killing any unfortunate civilian or vehicles to get in their way. Nexo warriors are alien cyborgs that are armed with energy flail, flickering energy nails and homing rocket launchers. Nexo walkers are large ants that walk around the streets and are eqqupped with plasma bolts, laser beams and electric shock for when players touch them, they die instantly, regardless of time stop or not. Nexo saucers with plasma cannons will show up to destroy players in their saucers.