So… the “Sonic Devastator,” eh? Knowing that I myself am not a superhero, here’s what I’d do:
First, I’d check for a timer or remote function. If there is one, which I’d hope there is, or triggering it while you’re holding it would blow your own ears out, I’d set it. When they’re looking for volunteers to pack their money, as is generally the case with big heists in a race to pack as much valuables as possible in a short window of time, I’ll make myself look available and slip it into one of the bags. After the robbery is over, and they start getting away… that’s when it goes off. The noise allows the authorities (or whatever costumed vigilantes there are in the area) to find them from afar.