How do you detect unusual changes to date and time?

I've been thinking a lot about how I can solve this.

Let's say;

• The user opened the app, made a transaction then saved it.
• Later the user made changes to the system date (past or future) to do some unexpected transaction or let's say cheat or something else.

Now at this point, the app should be able to detect unusual changes to the system date and time, and notify the user to bring back the correct date and time or just block the transactions until further investigation. How can I possibly do that? Is there a way for such?

The app can be offline or online depending on the availability of the internet connection. Now, what I am thinking right now is to check the date and time of the last transaction and then compare it against the new transaction that will be made. If it was too old from the last transaction then the user made changes to the system date (this is for past dates).

The problem is what if the user made changes to the system date for a future transaction? It is also not guaranteed that there will be transactions every day, so if there is no transaction for a week then this can cause an issue where the app detects changes to the system date.

Any idea?