Blindvaults were a special form of chamber which was used to store objects of value, to protect them from attempts at stealing them.
These chambers were sensor proof, sound proof, transporter proof and all but impregnable, allowing individuals to store items with a high degree of security. They were designed and manufactured by the Ferengi, who naturally had a vested interest in keeping their valuables safe. Blindvaults were also sold to other species for similar uses.
The lock mechanisms of these devices was a kind of tonal puzzle which involved a sort of a subsonic word association game where a person keyed in a specific note in response to random prompts from the vault's computer. Without the correct combination, it was almost impossible to open a blindvault in a short amount of time.
In 2371, the Maquis raided a Cardassian vessel and stole its blindvault, believing it contained biogenic weapons; they were unaware that it actually contained a Bajoran Orb. (DS9 short story: "The Orb of Opportunity")