Input into a PIC

This might sound like a real noob question, but I dont want to blow up my PIC so hear goes.

I have a PIC18f452 and want to use a smoke alarm siren to trigger an interrupt.
Not having a scope, or a multimeter with peak capture functionality, I set the alarm off and read the voltage on one of the piezo wires - reading about 3.5v

Now, how would you suggest connecting this to a PIC??

I was planning on connecting it in parallel so the siren sounds and hte PIC sees an input on a pin, but someone suggested I use a transistor to buffer it.

Any ideas?

Just feed it via a series resistor directly to the PIC pin, 47K should be fine - ensure the PIC pin has protection diodes on the pin you use, almost all do.