I don't want to use token, and will let everybody can fill the survey.
Well, that you could have mentioned before. This is quite an essential information to your request.
I don't see a reliable way to prevent someone that you don't know from participating more than once.
- Cookies can be deleted
- Cache can be cleaned
- IP addresses change.
- etc.
If I really, really want to fill out a survey twice, there are ways to get around basically all possible measures that do not involve token/passwords, even if you would prevent certain IP addresses from taken part more than once (which I think is a bad idea, because in many cases more than one person might be sitting behind the same IP address - more people in the same household, same company, university, etc.).
E.g. even if you limit my participation via IP address, I could take part from home, via mobile phone connection, at work 2x because I have two different internet providers and if I really, really want to fuck your survey up, I can switch off my modem at home and it will get automatically a new IP address. Oh, and I forgot, there is something called VPN...
So there is no way directly in LS to prevent more than one response per IP (which I also consider a bad solution because you exclude students from the same university, employees at the same company and other household members), and it would be a considerable effort to custom code this, I guess.
What you could do is to save the IP address and some other information like Browser version, OS version, etc. to create some kind of digital footprint. Then you could exclude responses that come from the same IP address with the same digital footprint. But this still does not guarantee that one person doesn't participate more than once.