Nexus 5 comes with a beautiful multi color notification light. This can be used to notify events when the screen is off. This feature is disabled by default and can be enabled from here:
- Goto Settings -> Display
- Check the tickbox option next to “Pulse Notification Light”
You might need to configure the color of the light, frequency and other options in the specific application’s settings(like Whatsapp and Gmail), for which you want the notifications.