I just published an Android app on Google Play Store, named "Contacts' Urgency".
This app allows you to set five different vibration patterns for your contacts' incoming call or SMS. These patterns represent five urgent priorities from one (lowest) to five (highest).
You may get confused and may ask the following questions:
Q1: How do you design these vibration patterns?
A1: Basically, for common smartphones, the strength of vibrator is fixed, and what we can change is when to turn it on and when to turn it off. Therefore, we define the vibration patterns as different combinations of four units: short on, short off, long on, long off.
Q2: How many levels of urgency can users distinguish? Why five? Why is one pattern more urgent than another?
A2: We conducted experiments to answer these questions, as shown in the following video.
For more details, please refer to our CSCW 2013 paper, "Designing an Effective Vibration-Based Notification Interface for Mobile Phones".
If you are interested in this app, please give it a try. Any comment or suggestion is welcome.