Another alternative for those of us with an unused antitheft device plug is to wire the buzzer into to the mating cap. On my 2018 Sprint 150 that's a TE AMP Multilock .070 8-position cap; the part number is 174931. I got mine from
Digikey. The part number for the pins to crimp to the wires is
345210-1.
You can then slip this onto the antitheft plug and the job is done. Easily removed if you or a future owner decide you don't want it anymore.
The antitheft plug does not offer a convenient way to wire the buzzer into the brake light as jimc recommends, however.