version 1.2.0 has been pushed to blockland glass pending approval.
seatbelt chime has been added but is disabled by default, it can be enabled by setting the pref $Seatbelts::SeatbeltChime (server.cs) to true.
it also turns out tumble wasn't actually being applied to all players during a collision, found this out while adding seatbelt chimes - this is fixed along with some minor code cleanup as well.
EDIT: update has been approved.