The total number of registered components that can be connected to the Gen 3 Base Station at one time is 99. This includes sensors, Keypads, Key Fobs, detectors, Smart Locks (each Smart Lock takes up two component slots, one for the pin pad and one for the lock) and Outdoor Cameras. 

SimpliCam indoor cameras and Video Doorbell Pros do not count towards the 99 as they do not connect to the Base Station.