Radar Sensor & Chirping Siren

Need recomendation on a soft chirping small size siren, what brands and models are available. Thinking to wire the radar sensor to this siren so it will only emit soft chirp instead of activating the alarm. Is this doable or complicated?

I'm looking for a type of buzzer (which is not as powerfull as siren) to be wired with the proximity (radar) sensor. Every time that radar sensor triggers it will alert via this small buzzer only. Most likely it will be mounted somewhere into engine comartment. I have BMW factory alarm and it does not have chirping option as warn away so I don't think radar sensor can be wired into this alarm. Will radar sensor work this way?

You could wire the momentary output of your Proximity Sensor to a Variable Timer (Peripherial's VT3 for example, or design your own) of some sort, and then have that timer fire a relay that activated a piezoelectric buzzer.

The result would be a BUZZ of predetermined length.

1. Is PAC TR-7 good fir this? 

2. What will  happen if I just wire the radar sensor's trigger wire directly to the alarm siren, will it provide plenty of power to chirp the alarm siren?

The PAC TR-7 seems like it would do the trick.  Here's the company's statement on that though:

http://www.pac-audio.com/products/productsCatagory.asp?mmSearch=Trigger%20Modules

Don't know the answer to the siren Interface question.