Sonic Bomb Alarm Clock Clock On Different Frequencies?

Clock on different frequencies? - sonic bomb alarm clock

Hello Iam looking forward to this bomb threat buy Clock http://www.sonicalert.com/htm/clock.htm Sonic, but the problem of the United States and the United States is that the different voltage and frequency of HAV .. I am eager to get down transformer, but do not know how often, as I read that if the frequency is low, the clock runs slower .. at Amazon UK, but the seller does not answer
so that all ideas