This is the Compustar FT-SIREN-6T six tone siren.

130 dB across six selectable tones. The six tones matter more than they might seem: a siren that cycles through different sounds is far harder to ignore than one continuous note, which the human ear tunes out surprisingly fast.

Its size is the real selling point. At under 3 inches in every direction, it fits engine bays that have no room left for a conventional siren, which describes most vehicles built in the last decade.

Dimensions

2¾ x 2¾ x 2¾ inches

Want one that keeps sounding if the battery is cut? See the Voxx MBS battery backup siren.