Heartbeat Sensor

"Roach, check your Heartbeat Sensor."

- John "Soap" Mactavish, instructing Roach on the use of the Heartbeat Sensor.

The Heartbeat Sensor is an attachment used in Call of Duty: Modern Warfare 2 and Call of Duty: Modern Warfare 3. The attachment allows the user to track multiple targets, somewhat like the UAV killstreak, and similar to the motion trackers in the Halo games (though the latter is a 360 degrees detector with immediate update, built into the armor) and notably, to the motion tracker in the movie Aliens. It displays the positions of people who are fairly close to and in front of the player.

Campaign
In the campaign, the display screen can be folded out from the side of the weapon and folded back in again. The first time it is used is in the level "Cliffhanger", where Roach finds himself in near white-out conditions. It is used also in the levels "Contingency", mounted on two M240s, and in "Just Like Old Times" where a ACR with Red Dot Sight, Silencer and Heartbeat Sensor can be found. The sensor likely uses the electromagnetic field created by the heart to discern personel locations. It probably uses an IFF system to tell the difference between friendlies and enemies. Friendlies are blue dots and enemies are white. In multiplayer games, friendlies appear as green dots instead of blue and enemies appear as red dots instead of white.

Multiplayer
The tier two perk Cold-Blooded cannot bypass the sensor, only the tier three perk Ninja can. The EMP killstreak will render it inoperative for the duration of the killstreak so that only static can be seen on the screen. This attachment is compatible with Assault Rifles, Light Machine Guns, and Sniper Rifles. It is also seen on the AA-12 in a few Special Ops missions such as "Acceptable Losses". To unlock the Heartbeat Sensor the player must get 15 suppressed kills with the weapon.

Overall, when analyzing its advantages compared to disadvantages, it's best to use the Heartbeat sensor as a reference and to continue checking the minimap and the player's perception at constant intervals.

Call of Duty: Modern Warfare 3
The Heartbeat Sensor will return in Call of Duty: Modern Warfare 3.

Advantages

 * The Heartbeat Sensor allows the user to locate non-firing enemies without the use of a UAV. This makes it useful in Hardcore, where there is no minimap without a UAV, or when a Counter-UAV is airborne.


 * Unlike the UAV, the Heartbeat Sensor can detect players using the Cold-Blooded perk.


 * It is especially effective for snipers to have this equipped as it can alert them of an approaching enemy, by sound and visually, unless said enemy is using Ninja and/or is coming from behind.


 * Consider using Scrambler and Heartbeat Sensor, the enemy will have a jammed radar and come searching for the player, but the player's sensor will find out where the enemy is.


 * The Heartbeat Sensor helps its user locate enemies through any obstructions, such as walls and smoke screens. This is why it works well with the FMJ attachment.


 * When used by one member in Team Deathmatch who has a microphone, it can be useful when going into buildings after players who are hiding. The person with the Heartbeat Sensor can pinpoint and call out their position of the player(s) to his team.


 * A player can use the Heartbeat Sensor effectively even without looking at it, as the Heartbeat Sensor beeps when it detects enemies.


 * While using the FMJ attachment, the Heartbeat Sensor makes the perfect assistant in performing unexpected penetration kills. This serves as a simple strategy for unlocking extended magazines on assault rifles and light machine guns.


 * On Sniper Rifles, the attachment can allow a sniper to find an enemy with ease; all they have to do is find the elevation to shoot.


 * The Heartbeat Sensor does not require a killstreak to activate and is active indefinitely, unless the enemy launches an EMP.

Disadvantages

 * There is a fairly long period of time (slightly longer than a UAV) between sweeps.


 * Many players often use Ninja (Pro) to counter the players that use headsets, while also countering Heartbeat Sensors.


 * When reloading a Grenade Launcher, the Sensor will obstruct the middle of the screen.


 * Enemies with Ninja will be able to easily surprise someone using the Heartbeat Sensor. This makes the Heartbeat Sensor less effective for Search and Destroy.


 * This attachment is almost useless in third-person, because the player cannot see the sensor, but can hear the beeps.


 * Players using a heartbeat sensor can inadvertently give away the positions of their teammates, if the victim watches the shooter's Kill-Cam.


 * In single player, the display cannot be seen while using night vision goggles. The sensor will glow brightly making it impossible to see.


 * The sensor only scans the area in front of and to the sides of the player (180 degrees). Enemies behind the player cannot be detected if they are directly behind the player.


 * In two-player splitscreen, the Heartbeat Sensor is off the bottom of the screen on some guns (mainly LMGs), making it almost useless, and a waste of an attachment. In three-player splitscreen, only the last player will experience this.


 * The sensor can be very confusing in multi-story buildings as it will beep even if the opponent is on a different floor.


 * Sprinting will obscure the player's view of the Heartbeat Sensor.


 * If the player is using Bling with the Shotgun attachment, the Heartbeat Sensor is not fully visible while the shotgun is readied on any assault rifle other than the M4A1, the M16A4, and the F2000.


 * Heartbeat Sensors can pick up enemies through surfaces and may misguide the player as to the enemy's actual location.


 * Enemies are able to hear the player's Heartbeat Sensor beeping, which can draw them towards the player and possibly reveal the player's position.

Trivia

 * The Heartbeat Sensor is one of the most frowned upon attachments of the game due to its ability to detect most average players (the exception being those using Ninja), regardless of UAV status or the use of Cold-Blooded. Many players don't believe that they should have to waste their third perk just to counteract the Heartbeat Sensor. Some online players have even disparagingly nicknamed it the "Baby Monitor".


 * Contrary to popular belief, the unused side rails on weapons that can't equip the sensor aren't actually evidence that the player could have been able to equip them. The Heartbeat Sensor model has its own rail, and it will appear on every weapon attached. This can be seen easily with the AUG HBAR, as it only has rails on the top.


 * The Heartbeat Sensor does not pick up the heartbeat of chickens. This was likely done so as not to confuse the player.


 * While reloading an M240 with a Heartbeat Sensor, the player's character closes the sensor before the reload animation begins, and re-opens it when the reload is done.


 * Civilians appear as blue dots on the heartbeat sensor.


 * The Heartbeat Sensor has a smaller range of detection in multiplayer. This was done for balancing purposes.


 * In Just Like Old Times, the player can pillage weapons from Shadow Company equipped with Heartbeat Sensors that, strangely, display SC soldiers as unidentified (hostile) contacts. This is strange, since their own weapons should light them as allied contacts, this was probably done as to not confuse the player.


 * The Heartbeat Sensor is very hard to use in split-screen mode because the screen is smaller. Only a few weapons will show the whole screen, such as a Barrett .50cal or M4A1 while other weapons such as the SCAR-H or FAMAS don't show the screen at all.


 * When aiming down the sights with the TAR-21 with a MARS Sight and the L86 LSW with Heartbeat Sensor, the Heartbeat Sensor remains almost entirely visible. This applies to the M16A4 with the holographic sight


 * The amount of the Heartbeat Sensor seen while aiming down sights depends on the size of the screen. Wide screens will have better visibility if the sights are close enough to the sensor (like the weapons stated above), though many weapons' sensors are off the screen to the bottom.


 * If the player never folds out the Heartbeat Sensor at the beginning of "Cliffhanger," Soap will never explain what the blue and white dots mean.


 * In Battlefield: Bad Company 2, one of the characters, Sweetwater, makes a remark about how General Braidwood will send "some Special Ops douche bags with pussy-ass Heartbeat Monitors on their guns instead of us." He says this during a mission that takes place on snowy mountains while recovering a piece of a crashed satellite, which is extremely similar to the scenario in "Cliffhanger".


 * The Heartbeat Sensor on the M240 in "Contingency" can't be folded unlike the ACR in Cliffhanger and Just Like Old Times.


 * When viewed in 3rd person with a sniper scope, one can clearly see up and down arrow buttons, as well as "Menu" and "Power" buttons. There are also small speakers and writing that says "Motion Tracker MT-33".


 * The Heartbeat Sensor will not detect friendlies using the Ninja perk.


 * When on a player's back and viewed from 3rd Person, the Sensor will appear completely white.


 * The reload and pickup animations are slightly different when using a heartbeat sensor on a SCAR-H or a F2000.


 * An easy way to obtain this attachment for Sniper Rifles (usually unseen due to needing kills with a silencer) is to attach a silencer to the player's sniper rifle of choice and play Hardcore game modes where the damage reduction is not an issue.


 * A cord can be seen running from the AUG HBAR's heartbeat sensor. This can be seen while reloading the weapon. This can also be seen on the M21 EBR, M16A4 and F2000 in multiplayer.


 * The Heartbeat Sensor on the M21 EBR is not camouflaged with the rest of the gun.


 * When the player is killed by someone with a Heartbeat Sensor and has Ninja, the Killcam will show them on their killer's Heartbeat Sensor regardless if they had Ninja or not,