A common method for vessel detection (primarily for collision avoidance) in the marine industry continues to be AIS (automatic identification system) in combination with radar. As part of AIS, each vessel transmits position, course, speed, and a unique signature that is received by other nearby vessels. As you can imagine, these systems are very accurate but also very expensive.
Hydrophone arrays and advanced camera systems are some of the lower resolution solutions available for detecting and tracking boat traffic from a single vantage point in areas like bays and waterways. Both are still relatively expensive, require a significant amount of data processing and consume enough power to require an expensive solar energy/battery system.
The BoatDetect device delivers a low power boat detection method at a fraction of the cost of existing systems. The caveat being that the BoatDetect device only has the resolution of detecting whether or not a vessel is in the vicinity. Even so, this level of resolution can still be useful to conservation groups and individuals who operate under a limited budget.