One would have to run the numbers before coming to that conclusion. A gyro spinning in a vacuum is very efficient and Li-ion battery amper-hour rating are quit

One would have to run the numbers before coming to that conclusion. A gyro spinning in a vacuum is very efficient and Li-ion battery amper-hour rating are quite impressive (meaning it could be small) Even something like an actuator that rises up over the thumb to indicate an object might be better than an audible tone. In the city, traffic could easily swamp your little speaker. The thumb could rest on the actuator and have 5-degrees of freedom. Woot.