A Steady Green Signal

I followed a faint low-frequency hum behind the black wooden cabinet. The space back there is narrow, quiet, and dim. Between a bundle of braided cords, a small rectangular box was resting flat on the floorboards. On its side, a tiny green light blinked once every few seconds. I placed both hands firmly on the casing to steady myself and waited. Five pulses. Ten pulses. The timing did not waver. I stayed beside it until the rhythm was memorized.