听到 is a resultative verb compound: 听 (to listen) + 到 (to arrive at) = 'to hear', meaning successfully perceiving sound. Unlike 听, which focuses on the action of listening, 听到 emphasizes the result of actually hearing something. You can insert 得 or 不 between the two characters to form the potential complements 听得到 (can hear) and 听不到 (cannot hear).