The simple answer is to plug them in, listen and determine if they are ruined. It will be fairly obvious if they have been damaged once they are turned on. Also, look at the drivers to see if they have been hurt in any way.
My only suggestion is to move your hi fi system to a room your housemates don't really have access to, like a bedroom. I went through a similar situation, only my roommate never damaged anything because my stuff was always in my room instead of a main living room
My only suggestion is to move your hi fi system to a room your housemates don't really have access to, like a bedroom. I went through a similar situation, only my roommate never damaged anything because my stuff was always in my room instead of a main living room