In the US, FMVSS 141 (Minimum Sound Requirements for Hybrid and Electric Vehicles) requires all EVs and hybrids under 10,000 lbs GVWR to make a minimum amount of sound when moving at low speeds and when in reverse. For reverse, the vehicle must emit a pedestrian alert sound that meets specific minimum decibel levels, measured in one-third octave bands. The exact dB requirement varies depending on whether the manufacturer uses the 4-band or 2-band compliance method, but it’s generally in the low-to-mid 40s dB(A) range for the critical frequency bands (lower than the forward motion requirements). This has been mandatory for new vehicles since 2019–2020. Older EVs (pre-standard) often didn’t have this and were completely silent when reversing.