After updating to macos sierra it seems seil and karabiner do not work any more. From the official site it looks like it will take a while before the replacement app karabiner-elements is ready for prime time.
1) Start Karibiner and take a screen shot of your current settings. Check off 'Show enabled only'
2) Uninstall seil and karabiner.
I found that macos would not shut down cleanly after this step. Like it was failing on closing a process and hanged. Seems to have went away after installing karabiner-elements.
3) Install karabiner-elements and create the file ~/.karabiner.d/configuration/karabiner.json
https://pqrs.org/latest/karabiner-elements-latest.dmg (mentioned in the above github README.md)
4) To get back my settings I added the following remaps.
"name": "Default profile",
5) To get the names of keys to add to the above, you can't really use the karabiner event viewer app. I was seeing Command_L and Fn. The following file has a list of all the acceptable names. control-f for left_command and you can see other ones that might suit your needs.
Hope this helps.