No, Truecaller cannot detect a person's availability if their mobile data is off. Truecaller works by accessing and analyzing the contact information and availability status of its users through their mobile data or Wi-Fi connection.
When a person has mobile data turned off, their device won't be actively connected to the internet, and therefore, Truecaller won't be able to fetch updated information about their availability or status. Truecaller relies on real-time data and connectivity to provide accurate information about a user's availability and presence.
If a person wishes to be available on Truecaller, they need to have an active internet connection so that the app can update their status and share it with other Truecaller users. Without an internet connection, Truecaller won't have access to the person's current status, and their availability information won't be available to others on the platform.