Why do computers use binary, instead of ternary, or some other logic system? In binary a unit (bit), can store 2 separate values. 

if you have ternary, then a unit can store 3 separate values.

why then don't computers use higher bases, for example in ternary you could have 3 different voltages, and even if transistors got a little bigger, wouldn't it still be more efficient?
3 different voltage levels makes building circuits harder and it is easier for little errors to occur in the signals.
Circuits need complex logic instead of the easy boolean logic which works perfectly.
Ternary is not compatible with binary that all computers use.