I am guilty. Because I have a new car, I havent checked pressures in about 6 weeks. Tires were set 6 weeks ago at 40/38. Today I had them checked and they were at 35/33. I was shocked! That is a 5 pound drop in about 6 weeks. Temperatures were a bit cooler this morning but I didn't realize how much temperature can affect pressure and probably how tires lose a pound or 2 pressure just as time goes by, say in a month or so. Moral of story is: check your tire pressure regularly, especially this time of year as temperatures drop. I'm sure I wasted a gallon of gas or more over the last couple of weeks. I certainly am going to check it more often.
Does it matter JMD? lol The tyre pressures can change with significant changes in outside temperature. Always good to get into a habit of checking them fortnightly at least.
The rule of thumb is for every 10° Fahrenheit change in air temperature, your tire's inflation pressure will change by about 1 psi (up with higher temperatures and down with lower).
Its in the manual, button is under the dash left of the wheel. Push and hold till you get flashing indicator on the dash. You could also pump them up to 42-43, then reset, then lower to 40, then it will warn you sooner.
FYI Tire pressue is sensitive to atomospheric temperature. Example if you have a fall weather cold front move thru your local area which is happen here you will realize some tire pressure loss. I am not fan of early TPMS systems the tire valve insert monitor is a hassle. I find for me far more easy to just rotate tires and routinely check my tire pressures......
Nitrogen mix has been claimed to better maintain tire pressure than just shop air pressure...........