Hearing Impaired strobe indicator triggered by a speaker tone.

I have a device that I want to trigger a strobe doorbell with when it sends out a one second tone. It also sends out a half second tone which I want it to ignore. With the help of the Internet, I assembled the circuit to trigger on the one second pulse with a 555 timer hooked up as a mono stable vibrator. This will help alert a hearing impaired employee know that a signal was delivered by flashing a strobe light.