Summary1. Behavioural research in deep water (>40 m depth) has traditionally been expensive and logistically challenging, particularly because the light and sound produced by underwater vehicles make them unsuitably disruptive. Yet, understanding the behaviour of deep-water animals, especially those targeted by exploitation, is important for conservation. For example, understanding interactions between animals and deep-water fishing gear could inform the design of devices that minimize bycatch. 2. We describe the 'TrapCam', a self-contained, high-definition video system that requires neither the support of a vessel once deployed nor special equipment to deploy or retrieve. This system can record 13-h videos at 1080p resolution and is deployable on any substrata at depths of up to 100 m. The system is inexpensive (<$3000 USD), versatile and suited to the study of animal behaviour at depths inaccessible to scuba divers. 3. We evaluate the performance and cost effectiveness of TrapCam and analyse videos retrieved from pilot deployments to observe spot prawn (Pandalus platyceros) traps at 100 m depth. Preliminary analyses of animal-prawn trap interactions yield novel insights. We provide future directions for researchers to use this type of camera system to study deep water-dwelling species around the world.