A boat ladder alarm system for a foldable boat ladder having a base rail and a movable rail is disclosed. In one embodiment, the boat ladder alarm system includes a first bracket, a second bracket, and a sensor system. The sensor system is configured to trigger an alarm when the first bracket and the second bracket are unconnected and to turn off the alarm when the first bracket and the second bracket are connected. In this manner, if the foldable boat ladder is unfolded and someone is trying to climb on the boat, the alarm is triggered to warn the boat operator that it is not safe to turn on the boat engine.