Question about Gigaset CL660HX Duo (DE version)

Yes, the Gigaset CL660HX DE version works with a Swisscom ST6840 DECT router, as it is compatible with standard DECT/GAP bases and routers. The Gigaset manual confirms that the HX handset can be used with DECT routers from other manufacturers, including via the DECT/CAT-iq 2.0 standard. Check the exact compatibility on https://www.gigaset.com/compatibil... and make sure that the router is configured for DECT.