At the beginning of the round, a random Terrorist will be given the C4. However, if a human player is playing with bots, and the settings are set to “bots defer goals to humans”, only human players will be given the C4.
In Counter-Strike and Counter-Strike: Condition Zero, the Terrorist carrying the C4 will have a brown backpack on their back. In Counter-Strike: Source and Counter-Strike: Global Offensive, the bomb will appear strapped to their back.
When playing as a Terrorist or as a spectator, the scoreboard will show the word “Bomb” next to the name of the Terrorist carrying the bomb. In Counter Strike: Source, the scoreboard shows a bomb icon next to the name of the player carrying the bomb. If the bomb carrier is killed or if he has dropped the bomb, the HUD on Terrorist player will show “(player name) dropped the bomb”. If another terrorist player picks up the dropped bomb, the HUD will say “(player name) picked up the bomb”.
The C4 can be dropped and picked up by other terrorists. If dropped in Source games, a bright light can be seen. In the radar, there is a red dot (in CS 1.6 and Condition Zero) or the C4 icon in red and emitting a signal. For balancing reasons, if the C4 is dropped, only a Terrorist can pick it up and the bomb cannot be moved with explosions or when shot at.
On bomb defusal and Demolition maps, it can be only planted at a bombsite. After a certain amount of time (45 seconds by default or 35 seconds under a competitive ruleset), the C4 will explode.
To plant the C4 as a Terrorist, one must walk to a bombsite (usually indicated by the letters A or B and when the C4 icon is flashing), select it using slot5 or ‘use weapon_c4’ and the player will spend 3 seconds planting the bomb. Note that the Terrorist cannot run, walk or jump during this procedure.
When planted, the C4 will emit a loud beeping noise that gradually increases in tempo. CTs must then defuse the bomb in order to win the round, regardless of whether any Terrorists are still alive. The time it takes to defuse C4 is 10 seconds or 5 seconds with a defusal kit.
In CS:GO, an update on November 6 revamped the C4 so that the code typing sounds after the initial planting sound are client-side. This makes fake planting possible. This was implemented to assist balancing the sides.
Only CTs can defuse the bomb. To do this, one must walk up to a planted bomb, look at it and hold the “USE” key for 10 seconds (5 with defusal kit). If the player shifts their field of view too far away from the bomb, stops holding the “USE” key, or reloads(in older games), the defuse is stopped and any progress is lost. Because of this, the CT who is defusing the bomb is an ideal target to attack and similarly important to defend.