Can I use WIFI as a primary communicator on the LYNX L5100, and a GSM cellular communicator as a backup?

A GSM Cellular Communicator is always recommended to be used as a primary communicator for your security system.

Cellular Communicators are more reliable than internet (IP) communicators. If IP communication should fail and your telephone wire become damaged, a cellular communicator will still keep your system connected to your central monitoring station.

Dual-Path is the way to go.

Since most households have available internet connections, it is suggested that you consider the benefits of a dual-path system. Backing up your system with two additional lines of communication (Internet and Cellular) creates a nice safety net that will help protect you and your family. For instance, if there were to be a problem with cellular communication, the IP communicator could still bridge a connection between your system and central station. Not only that, but IP communicators work better with remote control and video features because of their ability to create a more efficient path for sending larger bandwidth.

However, if you are certain that you want WIFI to be your primary communicator, then you must install the Honeywell L5100-WIFI. Getting GSM connectivity for the L5100 requires the installation of cellular communicator.