PSR600 close call and driveway alarm

I've got a wireless driveway alarm I am trying to find the frequency for. I have a PSR600. From what I have been able to dig up there are a lot of posting about 433 or 315 mhz. I did a search limit of 433 to 434 and 315 to 316 but hear nothing. I was hoping there would be something like 'close call' or a frequency counter. I don't understand the difference between Sweeper an limit search. It's a Chamberlain CWA2000 transmitter. It is not Murs