Probably not a new technique, but this is interesting:
https://github.com/outlandnish/poc-vpn-detection
This detects if you are using a VPN or not by comparing the time zone reported by your web browser with the time zone of your IP address.
So: remember to change your computer timezone to match your VPN 
Choose a country above or below you!
well, what if i am usin a vpn that is located in the same country as mine
Interesting. It definitely seems like something that would be taken into consideration when deciding whether an IP is a VPN/proxy. I doubt it could be the sole decider though. Detection these days is mostly from data leaks and figuring out if the IP is or has ever been a known exit point for a VPN/proxy. Once it’s fingerprinted, the detection gets easier. Do a WhoIS on an IP from a VPN and it’ll tell you who the provider is. You could also scan the IP using detection sites like ipqualityscore to find out what kind of information is actually being put out there.
You can have more accurate way to detect VPN using API such as https://www.ip2location.io
Then this is not something you have to worry about.