Hi Logan,
if your site is 3.2 or higher, you can achieve this by going to Site administration > Mobile app > Mobile features. You'll see a "Force log out" setting in there. If you enable it, the users will have to input the password everytime they access your site.
If your site is older you can achieve the same behaviour by installing the plugin Moodle Mobile additional features. In this case the setting is in Site administration > Plugins > Local plugins > Moodle Mobile additional features.
Kind regards,
Dani