What is the ruling on devices left in maintenance shops for months or years by their owners?

What its owners have left due to disinterest, there is no harm in taking and benefiting from it. As for what you do not know if its owner has no interest in it, it is a trust. If it is possible to communicate with the owner to return it or to know how to dispose of it, then that is obligatory. If the owner is unknown and there is no hope of reaching them, then the useful devices can be placed in permissible public utilities, or sold and their price given in charity on behalf of their owners. It is permissible to take the deserved fee from its price upon selling. These devices should not be held back, as that would diminish their value. Rather, they should be used for good and charitable purposes when there is no hope of knowing their owners.