What is the maximum number of motion sensors (wireless devices) that can be linked with the SK626 siren?

Up to 16 wireless devices (motion, contact, water, temperature, and power sensors, remote controls) can be linked to the  siren SK626. 

If more wireless devices are needed, consider using a dialer hub such as the  SK618, which can be linked with up to 23 sensors and 8 remotes. You can then use the hub to trigger the siren. It means you could link the dialer SK618 to the siren SK626. Once the dialer is triggered, it will trigger the linked siren.