Minimalist in size, not in performance! A Nano alarm is packed with features. Volume, tone and sensibility are adjustable. You can even set how long the LED should light up (from 10 to 40 seconds) by pushing the tone (T) button.
 
Of course, it features a 1:1 transmission and the reach is 100m. LED colors: red, yellow and green. Requires a A23 12V battery, which should be enough to last a whole season. Battery not included.