Why do crickets chirp at night?

Answer: Males calling for mates

Staying awake together — Wrong. Crickets don't chirp to keep each other awake. The sound is specifically a mating signal from males to females.

Males calling for mates ✓ — Correct! Only male crickets chirp—they rub their wings together (stridulation) to attract females. The chirp rate increases with temperature (you can estimate temperature by counting chirps!). They chirp at night because they're nocturnal and it's safer from predators.

Warning of danger nearby — Wrong. Alarm calls sound different. Courtship chirps are rhythmic and musical. Crickets do have warning signals, but the repetitive night chirping is for mating.