The new High Alert perk can now be unlocked in Call of Duty: Mobile as part of an event called Vigilance in Season 10 (The Hunt). The event has just started and includes relatively easier challenges to complete and get this new perk as the reward. Perks are power-ups that you can attach to your loadout and it helps in defeating opponents in Multiplayer matches.
This perk was first launched in Call of Duty: Modern Warfare as a tier 2 perk, but it soon became very popular. It gives a quick second chance to swiftly take an action and take down the enemy. In COD Mobile, this perk was initially spotted in one of the Season 9 test servers but it is finally launched to the public in Season 10.