The correct answer is option 4, ultrasonic sounds.

Bats have a unique ability called echolocation, which allows them to navigate and locate objects in their environment by emitting high-frequency ultrasonic sounds. These sounds bounce off objects in their surroundings and the bat listens to the echoes to determine the location, size, and shape of those objects.

By analyzing the echoes, bats can detect their prey, such as insects or small animals, even in complete darkness. The ultrasonic sounds they emit are at a frequency range that is beyond the range of human hearing, so we cannot hear them.

Option 1, infrared lights, is incorrect. While infrared lights are used by some animals to detect prey, bats rely on sound rather than light to locate their prey.

Option 2, ultraviolet lights, is also incorrect. Bats do not emit ultraviolet lights or use ultraviolet vision for prey detection.

Option 3, chemicals from their body, is incorrect. Bats do use scent and chemical markers for communication and finding roosting sites, but not for prey detection.

In conclusion, bats use ultrasonic sounds and echolocation to locate their prey at a distance, even in the darkness of night.