Satellite Tops Shifter (12 speed)
The new SW-RS801-T tops shifter was introduced when Shimano released Ultegra R8100 / R9200 to the world. It lets you shift your 12-speed bike from the tops, much like the older satellite shifters did.
These connect to the special Satellite Shifter port found on the 12-speed shift levers. This will be either the 2nd or 3rd port from the top (basically, the bottom port is always the satellite shifter port). They will not work in any regular SD300 port.
While previous satellite shifters were one unit, these newer ones consist of a shifting unit and a clamp, or band. In theory, you could actually stick the unit onto your handlebar using some strong double-sided tape,
Alternatively, slide the unit onto the band and then use the provided double-sided tape to attach it to the handlebar. You then use a tie-wrap to more permanently secure it to the handlebar.
These are sold as a pair, weigh 5.7g each and come with a 260mm wire.
These shifters will not work with 105 Di2 shift levers, since those do not have any extension ports.