Whenever a notification is received, vibrate the device with a morse code pattern of the first 3 initials.
Example
For example, if you receive a notification with the title "Hello, world!", the device will vibrate with the pattern "…. .--" (H W).
When receiving a chat message, usually the notification title is the name of the sender. So you can guess who sent the message from the vibration pattern.
How to enable
To enable: Settings → Apps → ⋮ → Special access → Notification access and enable dtinth’s Tools.