Orange County Floor Kitchen Bath

I re-piped my house myself. Everything with permits. Inspector checked it and he was happy (second time – not first time, but then I saved ton of money doing it myself).
Re-piping was part of another project – I am doing major remodel (new electrical, new low voltage, new piping, new kitchen, insulation, new bathroom, new drywall, new siding, new furnace / water heater etc).
Because repring is part of another project, I had walls open for some time. About a month after I run piping and passed inspection, I noticed that one of the t-shape connectors is dropping water – one drop every 30 sec or so.
I am going to fix it this weekend, but I have a more generic question:
What can I do to make sure all the connections are correct?
What can I do to alert myself if in future there is problem with one of the pipes? Is there some sort of hi-tech device that I can hide in the wall?

not sure why the kitchen water is still hot, but the 2nd bathroom is just luke warm. water heater seems fine, could the contracter messed something up in the line? The pressure is fine.

not sure why the kitchen water is still hot, but the 2nd bathroom is just luke warm. water heater seems fine, could the contracter messed something up in the line? The pressure is fine.

not sure why the kitchen water is still hot, but the 2nd bathroom is just luke warm. water heater seems fine, could the contracter messed something up in the line? The pressure is fine.

My brother in law’s unique solution to this problem was to remove the radiator, drill a hole in the slate and slide the slate over the radiator pipe, then re-install the radiator. Tedious but it looks great.