Then, edit the .csv file (e.g. using POI Editor or notepad) to include the location for speed alert, in following format:
Then use POI Loader for Garmin to load it into your GPS unit. Make sure you choose the right unit (Feet/Miles vs. Meters/Kilometers". The number after "@" will be the limit (at mph or kph respectively). The alert will appear when you are within 36 second * Speed, and appear if you exceeds the limit.