From what I know there's at least two pilots on alert at all times. That means you have to stay on base for the entire shift. Depending on the base layout, you may not be able to really leave the alert building. However you do have a bed, kitchen, showers/bathroom and gym typically at the alert building. Pilots rotate to sit alert along with their regular flying schedule. They are still required to get the same number of sorties in each month. The primary purpose of alert is to have aircraft that can quickly respond to an emergency. This means getting jets in the air in 10 minutes rather than the 45 minutes with live weapons, at least for fighters. You can make good money on alert and it is an AGR position but you have to realize you're stuck there. You're not in your own bed, can't visit your family, can't have a beer at the end of a long day, etc. As far as what it changes at a base, I'm not entirely sure. But I do know that based with alert usually do not deploy for longer than 90 days at a time due to the pilot rotation. And some pilots are only able to do half of that time because they need to fill in back home on alert otherwise the alert pilots would be unable to get their required sorties in.