I agree with calling in a tech, whether that’s a plumber or an HVAC technician, to review your set up. Two leaks in six months is way too many. It may be that all your pipes are about the same age and therefore you are seeing degradation that is going to result in many more leaks. We have radiant heating in our house, so this is an issue that has come up for us. Sometimes the pipe just need to be wrapped, sometimes they need to be replaced but I would definitely have somebody look at them.
Next as far as detecting leaks, you want to use a moisture sensor so that it’s not falsely set off by changes in humidity. No big deal, there are lots of those.
Now as far as maximizing the use of a single sensor, what is commonly done for ceilings are called trough pans or troughing systems. This is like a huge catch pan but the trick is that it is slightly sloped to draw the water to certain points and then you put multiple contact points any of which can trigger your actual Notification sensor. There are places that make these, or you may be able to make one for yourself. The concept isn’t that complicated once you’ve seen one. You have to decide what kind of walkways you want to leave in the area, but that just depends on the exact set up and where the pipes are.
Here’s one typical product:
This one cost $750 for a 64 square-foot tray, plus you have to pay for the notification sensor.
I’m not recommending that specific one, I haven’t checked out the company or anything, I’m just saying that’s a typical example and you could research that type of thing further if you think it’s something you would need.
But honestly for most residential installations, it’s just a matter of maintenance on the boiler system so that leaks become very unlikely.