In previous Call of Duty games, players earned killstreaks by getting a certain number of kills in a single life. Modern Warfare 3 introduced Point Streaks where players earn points by not just getting kills, but also by completing objectives, i.e. capturing Domination flags and planting S&D bombs, and by destroying enemy killstreak rewards, i.e. UAVs and Sentry Guns; these points in turn give rewards. However with Scorestreaks, players now earn rewards for earning a certain amount of score in a single life. This means actions like kills, captures, completing objectives, shooting down enemy air support, assists, and assists with certain scorestreaks count towards the earning of new scorestreak rewards. Like in previous Call of Duty games, the player's streak will reset upon death.
The player's Scorestreak rewards can be obtained multiple times in one life, but only if the player uses his/her scorestreak prior to receiving the same scorestreak again. For example, if the player earns the Swarm scorestreak, chooses to save it, and they earn the Swarm again, the first Swarm will be lost, being replaced by the second Swarm received by the player.
Unlike most previous games, dying does not impede progression by called in streaks. While any points gained are lost upon death (except in Call of Duty: Black Ops Cold War), the player may still receive points through streaks (most of them except UAV, Counter-UAV, Orbital VSAT and EMP systems assists) called in before being killed or by calling in streaks that they have saved up. As long as points are awarded after death, it doesn't matter when a scorestreak has been called in nor when it has been earned.
Using the perk Hardline in some games, the score towards the player's scorestreak is increased by 20% meaning this perk is extremely beneficial for obtaining the higher rewards. For example, if one was trying to receive a Swarm and was using Hardline, they would only require a 1585 scorestreak rather than 1900. This equates to three fewer kills in Team Deathmatch.
Using the Persistencetrait in Call of Duty: Infinite Warfare allows Scorestreak progression to continue after death, but the amount of score to obtain a certain streak is increased.
List of the Scorestreak rewards in Black Ops II.
In Call of Duty: Black Ops Cold War, progress towards each scorestreak is no longer lost upon death. The points required are much higher, but getting consecutive kills grants bonus points towards unlocking score streaks. All scorestreaks except Air Patrol have a cooldown to prevent being used to often.
Airborne drone that seeks out and destroys a nearby target. Adds 25 points per kill. Will also take out enemy scorestreaks (only UAVs, counter UAVs and care package couriers) for the appropriate amount of points if thrown in the right general direction.
Projects a microwave field which stuns, impairs, and slowly damages enemies. As the Guardian damages enemies, the player will earn 10 points per two damage increments (Guardian Supress). Adds an additional 25 points to the player's scorestreak per kill (Guardian Kill).
An air-to-surface missile which can be scattered into a cluster bomb while falling. Adds 25 points to the player's scorestreak per kill (Hellstorm Missile Kill). The missiles can be shot down by the enemy (only if the cluster is not yet deployed).
Launch a coordinated and rapid airstrike on three locations. Adds 25 points to the player's scorestreak per kill (Lightning Strike Kill). As of 1.4, there is a .9 second delay between call-in and arrival.
Air-drop an autonomous ground robot that searches for and destroys enemies. Can also be remote-controlled if the player would like to. Adds 25 points to the player's scorestreak per kill. As of the latest patch, mobility is increased and close range machine gun damage is decreased. The AGR is equipped with rocket launchers and mini-guns.
Call in a stealth helicopter which does not appear on the enemy's mini-map and is very distracting to enemies trying to take it down. Adds 25 points to the player's scorestreak per kill (Stealth Chopper Kill). Takes two shots to destroy.
Temporarily disables enemy electronics and HUD and destroys scorestreaks that are active at time of detonation. Also gives 10 score towards the player's scorestreak whenever a player on their team kills an enemy (EMP Assist).
Call in a swarm of lethal Hunter Killer drones that search and destroy enemies as well as enemy aircraft for the appropriate number of score. Adds 15 points to the player's scorestreak per kill (Swarm Kill). Lasts for 45 seconds, can be destroyed with EMP systems
In Call of Duty: Advanced Warfare, even if the player adds scorestreaks to the preset loadout for the Survivors in Infected mode in Private Match, they will not show up in the Survivors' loadouts during gameplay and will not be given to the players when they reach the required score amount.
In Call of Duty: Black Ops II, when the player reaches the required score to unlock a scorestreak or recieves one via a Care Package, a sound relating to the scorestreak will play, such as car noises for the RC-XD and radar sweeps for the UAV.