I spotted this in a newsgroup, it's for a 307 but it might be of some use? I have to be honest I don't think mine does anything if you press this button in but you never know.
Subject: Re: Bloody Beeping
From: "Steve Parker" <
steven.parker.NOSPAM@ntlworld.com>
Newsgroups: alt.autos.peugeot
Date: Sat, 01 Sep 2007 16:57:32 GMT
> I have a Pug 307 and when on the motorway It beeps at me when over
> 70 mph, I haven't really noticed it before as I don't travel on the motorway
> that much but the other day it was really getting on my nerves, Is there any
> way that I can de-activate this "feature".
Its caused by the trip computer. go to the instant figures screen and you
should see a key next to the speed icon. hold trip computer reset
button/stalk in and it should then come up with speed setting increase as
required.