Traps are relatively inexpensive structures that remain hidden until they are activated by an attacking troop moving into their trigger radius.
Once activated, traps must be re-armed in order to be a part of the next defensive Layout (with the exception of Clan Wars (including Friendly Clan Wars) and Friendly Battles, where all traps are active for every enemy attack).
Traps can greatly improve the effectiveness of a village's defense if properly placed. For example, if your village successfully repels an attack while you are away from the game, but several of your traps are triggered, any subsequent attacks will not have to deal with those traps until you re-arm them.
Although commonly thought of as a trap, the Hidden Tesla is not listed here as it actually a hidden Defensive Building and does not need to be re-armed for re-use.
Even though traps are classified as "Defensive Buildings", they are not buildings and do not need to be triggered/destroyed for your enemy to reach 100% destruction (nor do they count toward it).
Traps do not need a free builder to be placed or re-armed, but they do require a builder to be upgraded.
When the bombs are triggered and the battle ends before it explodes, it still remains armed.
Currently all permanent traps have upgrade levels, but the temporarily available traps have only one level and simply disappeared from players' bases when the respective events ended.
Upgrading is available as soon as the trap is bought from the shop.
Upgrade times are relatively short compared to building upgrades, taking at most 3 days to build.
Most levels of traps have a relatively low cost compared to buildings.
Different trap types have different upgrades: Damage, radius, etc.
Traps being upgraded are visible to enemies; it is usually a good idea to relocate them while they are being upgraded to ensure that enemies don't know where traps aren't. However, remember to replace them when it is finished upgrading.
Each trap must be upgraded individually. Upgrading one trap does not upgrade all traps of that type.
Attackers can deploy troops on top of traps even when they are being upgraded.
After a trap is triggered, it stays right where it was, but its status is "Triggered".
After a trap has been triggered, it needs to be re-armed.
You do not need an available Builder to re-arm the traps.
Once a particular trap is upgraded, it is permanently upgraded. Upgrade levels don't disappear when it is triggered.
Re-arming traps costs gold. Re-arm cost increases as the trap is upgraded.
You can re-arm all traps with one button at the Town Hall or by clicking one of your traps. You can also re-arm traps one by one if desired.
If a trap is triggered by one attack and not re-armed before the next attack, the triggered traps are not visible to the next attacker at all, and will not appear nor affect the battle in any way even if enemy troops move into its trigger range.