8 January 2016 Last updated at 00:45 GMT
The options include a breathalyser, a multi-coloured flashlight, an SD card reader and an air quality sensor. The Nexpaq case itself will cost $99 (Â£68) and its modules will range in price from $20 to $45.
Smartphones that come with the built-in ability to accept modules are already on sale and in development - but the advantage of this product is that it can be used with existing iPhones and Galaxy S6 handsets.
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A smartphone case is on show at CES that allows owners to add extra hardware modules to their handsets.