What options does LimeSurvey have, to limit the amount of finished surveys by person to one?

I know I can use Token and Cookie. I want the survey to be open, thats why token ist not an option for us. Cookies are easy to delete. Is there an option to limit it by ip-adress or via email that im missing?

There is not way to prevent someone to take part in an open survey more than once and thus Limesurvey has no measures besides cookies, which is an easy prevention for probably 95% of people, who have no clue about the internet and cookies. Now the other 5% are generally 'tough cookies' . They know how things work and they will for sure find a way to get around
1. Blocking used IPs could be a problem when you want to allow more than one person per family / company. Many companies and organizations (e.g. universities) have a fixed IP and all internet traffic going out is identified by this ID.
2. There are relatively easy ways to get around the IP as well:
- With most consumers it is just switching off the modem and switching it on again and the ISP will most probably give them a new IP
- I could do the survey at home, at work, via smartphone through 3/4G, in public Wifis, VPNs, etc.
3. Email: It is so easy to create emails, it is not even funny. With Gmail for example you can create aliases by using yourname@gmail.com and convert it into something like yourname+survey1@gmail.com, yourname+survey2@gmail.com, etc. and you can create as many aliases as you want, they will all go to yourname@gmail.com. Of course there are a lot of other options. Easy peasy.

So I guess all efforts will make little sense, if people really, really want to take part more than once. But as long as you don't offer a very huge incentive to anyone, chances are low that people are actually inclined to do it.

renebesicke wrote: or via email

Token with Allow public registration is done for this.
manual.limesurvey.org/Participant_settin..._public_registration