>I would advise against trying to do server side device detection. Build your UI so that it can adapt to device size or use media queries on the client to decide how style content differently.
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>There are a million combinations of user agents and if you skip new user agents you are bound to piss off people in the future.
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>And if you really do want to do this there are libraries natively in .NET as well as for JavaScript that let you get reliable and updated browser detection. If you use anyhting use that so the burden of keeping your user agents updated isn't on your code.
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>These days the only browser detection I ever do is to check for old version of IE (pre 10). Everything else is detectable with other means more easily and usually it's not the device you care about by the size of the screen (device-width).

Everything is controlled on the server. This is only for the setup of a single properly.