If you can make pro version. Example I am using same ip address for 1 month, if my ip changes, then it should send a code for login. example:
After login: We have detected new ip for login. We have sent a code to your email address. Please enter the code to login.
It will be better than Two-factor authentication because. Two-factor authentication everytime you enter again and again and thirdly once my phone was broken, and i lost all access to my logins. Very painful.