How to block mobile or smartphone browser access for clock in/out functions in asp.net

We've created a clock in/clock out page built using asp.net in vb, and we are trying to see how to add controls to block it for users trying to access the page on mobile browsers or outside networks.

We know we can restrict it to a single IP address, however, the organization the IP belongs to frequently changes their network IP  (as we've been told).

Any code set would be of help.

Please let me know if you have any further questions.

Thanks!