Stop spam SMS alerts by only playing a notification sound and vibrating your
phone for senders in your contacts.

To make this app work as intended, disable sound and vibration in your normal
Messaging app, and let this app do it only for senders in your contacts list.

If you are using a version of Android earlier than 4.4, you may like to try the
original ru.glesik.nostrangersms, of which this app is a fork.