tattler

noun

1. One who tattles (notifies authorities of illicit behavior) or is inclined to do so; a tattletale.

   “My sister is a big tattler; she always tells Mommy when I hit her!”

2. Either of two similar bird species in the shorebird genus Heteroscelus (Tringa in some taxonomies).
3. A device fitted to a vehicle to measure mileage etc.

   “A few truck drivers griped drowsily about the tattlers in their cabs which graphed the mileage per hour per day.”

   “Electronic monitors (black box, tattlers) help to define the actions of the driver during normal and emergent operation of the EMS unit.”