If something is confiscable, it is legally subject to being taken away by an authority figure. Whether it's a prohibited item at an airport security checkpoint or an electronic device prohibited in the classroom, a confiscable object is one you are at risk of losing.
The word confiscable comes from the Latin confiscare, meaning "to consign to the public treasury," and it's related to the English word confiscate, "to take possession of by legal authority." Confiscable items may be taken temporarily or permanently, depending on the situation, and they are taken when a rule or law has been broken. The word is usually associated with weighty legal matters, as in a getaway car being confiscable after a bank robbery. However, it applies just as well to cell phones being taken away in meetings where secret or classified information is discussed.