dgez has a point, although you would hear a leak if you kept the system charged to 30 psi.. Open up the fridge/freezer/keezer and listen for escaping gas. Make sure all the clamps are secured properly... You can even take the gas lock ends and put them into a container of water to see if they have slow leaks or not.
Although the easiest way to see if you have a leak is to simply charge the system (disconnect any kegs from the gas side) and then turn off the tank valve. Leave everything else as normal. If the regulator doesn't move (or does only as temperatures chance, if outside the fridge/freezer/etc.) then you're set. If the high pressure side starts dropping, then you know you have a leak that you need to hunt down. I would let it go a full 24 hours the first time to make sure you don't have a leak. If it comes back 100%, then you have other issues to address.