I check my tires every two or three weeks, or before/after a day on the road. I use a high-quality hand pump, and I carry one when I'm on road trips. If you need to use your spare tire, it's probably going to be low on pressure.

Topeak's "Joe Blow" line of bicycle hand pumps are great. They make some that are high-volume/low-pressure for mountain bikes and fat tire bikes that also work better for cars. My current low-volume/high-pressure Topeak pump is about 15 years old and working fine. I might treat myself to a low-pressure/high-volume model though.

https://www.topeak.com/us/en/products/41-Floor-Pumps/845-JOEBLOW-DUALIE

Most of Topeak's stuff is made in Taiwan, but some is made in China.

I have to pull my cars out of my cramped garage to check the tire pressures. I do this early in the mornings when the cars are cooled off and before sunlight can hit the tires (heating them up and increasing the pressure).

A bunch of the (other) geezers in Bubba Estates are out early getting in their 10,000 steps before it gets too hot. They always ask me "Do you have a flat tire?"

Using a separate high-quality gauge, I set the pressures so the gauge needle is right on a one-PSI hash mark. If one tire's pressure is significantly less than that of the other tire on the axle, I go looking for an embedded nail or screw and I always find one. I've caught a lot of slow leaks from embedded nails or screws this way, and I catch them when and where it's easier to deal with them.

Tire pressures go up or down about one PSI for every ten degrees F (Ideal Gas Law). I adjust the pressures to their "baseline" based on the average forecast low temperatures for the next ten days. If the average forecast daily low temperature is 65 degrees F and it's 75 degrees F the morning I check and adjust pressures, I and an extra one PSI.

I check tires more often in the second half of the calendar years, since the outside temperatures are decreasing. In the spring, I often have to bleed air out instead of adding it.