I found it's very annoy when my Nuvi 3790 keep alert me there's a Redlight camera at the intersection where I was stopping there at that light till I drove thru the light.
Is there any way i can set it to alert only once?
Yes when you install two gpi files in the Garmin both will speak if the have a voice embedded, you may have to back convert it to a csv file than use the poi loader to load it into the Garmin, that way you have control of the icon and voice.
Not too sure how you can created your own gpi file or edit it.
POI Converters will take a gpi file and convert it to a csv (been a long time since I have done that) and POI Loader will take a csv file and make a gpi file.
I have used both methods of installing the only difference is that with the gpi file placed in it works all the time while those loaded with the poi loader can be turned on and off through the Garmin (Haven't got it here but can tell you latter if required I think you have to work your way through settings to my data.