I just downloaded the same to my TomTom One (3rd Edition). In my Change Preferences (screen 2 of 5), I selected "Warn when near POI" and set the warnings for both Red Light and Speed Cameras (downloaded both). Also downloaded the sound files from this site and used those for my warnings. Seems to work great so far.
some of the Tomtoms have a bug that if your file comes with a sound file (ogg extention) the device automatically selects those sounds when warnings are enabled but you cannot hear them. An attempt to change the sound makes the device hang. The workaround is to leave the default choice alone, it would still sound right on the route. You could always change the sound file by renaming and copying to the card later if you need to.
First, you have to make sure that you are using one of the computer voices not just one of the regular voices. So if you are not using a computer voice you have to change it for the spoken alerts to work.
After you have done that follow the steps and you will have them up and running in no time.
1) Go to menu then click change preferences
2) Click manage poi
3) Click warn when near poi
4) In this screen locate your redlight & speed camera group & click it
5) Choose you alert distance I use 300 or 350 yards
6) After this you will have 4 choices
Full spoken warning
Brief spoken warning
Type in warning
7) Choose either full or brief spoken warning select done
At some point a prompt will come up asking if you want to only get alerts if they are on your route leave the box unchecked if you choose this box you will only get alerts if you have a route defined.
9) Now click done i believe 3 times and you are set.