Thanks to everyone that has weighed in on my project. From what I've heard from the kind folks here is that there's nothing "obviously" wrong with the circuit I've proposed, just that I, quite possibly, lack the experience to pull it off.
So, I've tried to take a second crack at the circuit based on the circuit posted a few posts above this one, using an already proven (and well explained) circuit at the risk of complicating the circuit and overloading my already feeble mind.
Digging through my tackle box, I was able to find a 3V relay amidst what I thought were all 12V relays (bonus!). Its like it was sitting there just waiting for me to find it for this project.
I have yet to build the circuit, but I do have some confidence that it will work properly. The only drawback is that I'm not sure it will fit into the battery compartment of the sensor module I am modifying, so it'll probably take a bit more planning on the mechanical side of things.
I've attached the circuit drawing. I removed the DPDT switch because I won't be needing to switch between activate on dark and activate on light. I'm now trying to understand Darlington Pairs and what that's all about, but I think I understand the basic premise...at least somewhat. Using a smaller voltage/current to switch on a transistor that can use a larger voltage/current to switch on a relay. Allows a much higher gain than with a single transistor. Not sure why its necessary in this circuit, but I'll keep pondering that question. Any light the folks can shed on this would help.
I'll be leaving the country in a couple days, so I don't think I'll have time to build it and test it before I leave. I may not have a good way to respond back to comments until I get back, so thanks in advance to the community for your interest and comments.
EDIT: I've written an instructable, more so that I can remember how I did it and keep track of my progress. I like how you can add comments to pictures and stuff. Anyway, the instructable goes through in detail what I didn't really want to clog up these forums with, so check it out if you are interested. I didn't want to publish it until I got things working flawlessly, but I think it would help those who are trying to help me to understand what I'm doing. I'd prefer to keep the comments in this thread on topic, which is specifically the sensor circuit, but I can start a new thread on the overall project if there is interest. PM me if this is the case. And yes, I've quite literally got a box-load of these cameras and sensors in the garage, much to my wife's chagrin.
Xanboo/Homesite Laser Break Beam Sensor
Regards,
Ken.