My BMX bike front tire went flat on me for no reason. My room wasn’t warm at all, but it was cold. I don't know if that caused it because only my front tire went flat not my back. Any suggestions? I don’t have holes in them.
You can try taking the tube out, add a little air, and then submerge it in water.
Sometimes it's easier to find a tiny leak when bubbles are coming out of it. There's a chance the leak is at the valve so check there too.
Just take care not to inflate the tube too much. Without the wheel and tire constricting it, the tube will expand much easier and you risk making the tiny leak into a ruined tire.
There's a hole somewhere. (there has to, or #3) Look for it by Henry's answer and check tire by Argenti's answer.
There's still a hole, and it's on the base of your valve. File down the valve hole on your rims. For extra measure, cut an old piece of inner tube or rubber strip, cut a hole a tad smaller than your tube's valve, and slot it on your valve. It'll function as extra protective layer. Also, if your valves are Presta or threaded-through Schrader, don't tighten you valve nut too much.
Your valve core's not tight enough (for some reason). Get a valve core wrench/driver and tighten it down.