Truecaller's Availability feature makes it possible for you to know if the person you're about to call is busy or not.
For example, if you see a red bell icon next to that number it means that phone is on silent mode. If you see a red phone icon, it means that person is on the phone.
You can also see the last time a user was active in the app through the ‘Last Seen‘ time displayed.
For more detailed information regarding the Availability feature, please visit our blog.
You can always turn the feature off or on in the settings section in Truecaller.
Please note: To be able to see someone's availability they must have Truecaller installed and have the feature on.
Availability is activated by default and can be disabled in Truecaller's Settings > Privacy Center