Breakable objects

Breakable objects are a type of collectibles featured in Batman: Arkham Asylum, Batman: Arkham City and Batman: Arkham Knight. These objects are to be destroyed with gadgets. They are thematic riddles that are well hidden by the Riddler; by destroying them, you solve riddles and gain experience.

Batman: Arkham Asylum
The only breakable objects in this game are Joker teeth. These are some sorts of mechanic or robotic sets of teeth that move around place and make loud noise. Usually they're distributed in various places, but they are also contained in "present boxes" supposedly placed by Jokers, which breaks open when you approach them or when you throw a Batarang at them.

Joker's teeth can only be destroyed with Batarangs (aimed, quick-fire or remote).

Joker teeth
Joker's teeth appear again, but this time rather late, around the time you start to learn about Joker's plan. They appear where in the tunnels leading to Wonder Tower. Destroy them with Batarangs, Remote Electrical Charges (RECs) (aimed or quick-fire) or Bolas.

Joker balloons
These are groups of four balloons (each of them counts as one balloon) with Joker's face drawn on them. They are tied to various spots in Amusement Mile and Industrial District. Destroy the by throwing Batarangs or Bolas, firing RECs, or simply making contact with them.

Penguins
These porcelain penguins can only be found in the Museum of Natural History, the Penguin's lair. They can be destroyed with Batarangs, RECs or Bolas.

Demon heads
Demon heads are emblems of demons with rings in their mouths. They can only be found in the Wonder Tower area, Ra's al Ghul's and Hugo Strange's lair. You can attach the Batclaw (aimed or quick-fire) to the rings and pull the demon heads off wherever they are.

Harley heads
These are the heads of Harley mannequins equipped with voice boxes that can be activated to play some of Harley Quinn's dialog. They are only in the Sionis Steel Mill, Joker and Harley Quinn's hideout. Destroy the with a Remote Electrical Charge (aimed or quick-fire).

TYGER CCTV cameras
These cameras that are found all over Arkham City. Their locations are not revealed on the map even if you have already interrogated all of the Riddler's henchmen. You can spot them easily, but you can also hack CCTV hubs in the respective district (this count as a riddle) to reveal their locations on the map. Destroy them with Batarangs, RECs or Bolas.

Harley balloons
These are single balloons with Harley's face drawn on them, found only in various places (indoor and outdoor) in the Harley Quinn's Revenge DLC and therefore do not count as riddles. Their locations are not revealed on the map. Destroy them with Batarangs, Shuriken or RECs, or by making contact with them.

Jacks-in-the-Box
These only appear in Panessa Movie Studios after Harley Quinn takes over it and there's music coming out of them. Throw Batarangs or Shuriken at them to make them explode.

Insect crates
These can only be found in the Stagg Enterprises Airships, where Scarecrow prepares the Cloudburst, and there's noise made by the insects trapped in them. You can break them by striking directly, or by pull the handles attached to them with the Batclaw.

Spider Drones
These can only be found in Arkham Knight's headquarters, and they make slight sound. They can be destroyed by a Remote Electrical Charge or by shots with either the 60mm Cannon or the Vulcan Gun of the Batmobile.

Militia shields
These can be found on the walls of buildings all over the streets of Gotham and in the service tunnels in Founder Island. They can only be destroyed by Batmobile firearms.