Swarm Whistle

Sym-Tech Item, uncommon (requires maintenance/attunement)
You must be proficient with wind instruments to use this whistle. While you are attuned to the whistle, creature swarms are indifferent toward you and will not attack you unless you threaten or harm them.
The whistle has 3 charges. If you play the whistle as an action, you can use a bonus action to expend 1 to 3 charges, calling forth one swarm of rats or other similar creature (see the Monster Manual for statistics) with each expended charge, provided that enough of those creatures are within half a mile of you to be called in this fashion (as determined by the GM). If there aren't enough creatures to form a swarm, the charge is wasted. Called swarms move toward the music by the shortest available route but aren't under your control otherwise. The pipes regain 1d3 expended charges after a long rest.
Whenever a swarm that isn't under another creature's control comes within 30 feet of you while you are playing the whistle, you can make a Charisma check contested by the swarm's Wisdom check. If you lose the contest, the swarm behaves as it normally would and can't be swayed by the whistle's music for the next 24 hours. If you win the contest, the swarm is swayed by the whistle's music and becomes friendly to you and your companions for as long as you continue to play the whistle each round as an action. A friendly swarm obeys your musical commands. If you issue no commands to a friendly swarm, it defends itself but otherwise takes no actions. If a friendly swarm starts its turn and can't hear the whistle's music, your control over that swarm ends, and the swarm behaves as it normally would and can't be swayed by the whistle's music for the next 24 hours.