Naturally, those inside are looking for a way out, and this is when most homeowners notice them. Crickets end up inside primarily because they're looking for a warm place to escape those cool, early autumn nights. When it's cool, they, like ladybugs and other insects, tend to conserve energy by slowing down their metabolism. You can get a feel for the temperature at night by listening to crickets chirp. The common field cricket sings by rubbing its right wing over its left wing.
Crickets sing at a slower rate when the temperature is lower.
Note that this rate is also dependent on the species of cricket. As the temperature drops, their exposed wings cool quickly. Most insects, such as crickets, have a large surface to volume ratio. Things with wings, long legs and extended thoraxes have a good deal of body surface area compared to their mass or volume. What this means is that on a cool evening, crickets are more inclined to find a place where their energy isn't transferred as readily to the environment.