OnePlus is offering its take on Valentine's day specials and is now bundling a free Rosewood case with OnePlus X purchases. What you need to do is enter the XOXO promo code upon checkout.
Alternatively, if you're after the OnePlus 2, you can get a Black Apricot StyleSwap Cover free of charge. The promo code for this one is LOVE.
A couple of caveats though. Only these two specific styles are part of the offer, one for each smartphone. If you've chosen a different case/cover, entering the promo code will add the correct one, deduct its price, but still keep the one you originally selected, so make sure you delete it.
Additionally, if for some reason you've decided that now's the time to get both the OnePlus X and OnePlus 2, you can't claim both promo codes in the same order. Also, the fine print contains the magic words "while supplies last", so make sure you act quickly.