Rather than making your event function return either true or false (or 1 or 0) that indicates whether the event function thinks an event has occurred, have it return a continuous value and let the ODE solver detect where that reaches / passes through 0.
For instance, in the documentation example the first events function appleEventsFcn does not return y(1) == 0 or y(1) < 0 which would be either false (0) or true (1). Instead it returns y(1). The ODE solver will evaluate the events function and determine the time when the event solver's first output has a zero crossing in the specified direction.
The other two events functions, bounceEvents and orbitEvents, behave the same way by returning a continuous value and allowing the solver to interpret the outputs.
