bln does not work with notifications which are turning on the display. So for SMS just use an app like GoSMS where you can configure the display to stay off, like in whatsapp.
Device: Samsung Galaxy S4 (GT-I9505)
Rom: Stock-Rom (I9505XXUGNE8)
Device: Samsung Galaxy S4 mini (GT-I9195)
Rom: Stock-Rom (NB3)
Kernel: Vikinger (BLN)