event detector feasability

I have a project where I need to detect a microsecond break in a dc signal. Given that the clockspeed of an arduino is in the MHz, would a loop that looked for a low signal, then kicked out a signal to turn on an LED be able to pick up such a short break? Thanks.

That's what interrupts are for. Can detect a signal that is I think 2 clock cycles in duration (0.125uS).

Thanks! Just the answer I was looking for.