Even though serving on a jury is an individual's civic duty, it's never a pleasant thing to rush down to the courthouse at dawn and wait, and perhaps never be needed or selected. In order to minimize this, some courts use the standby system. This is a method of ensuring that enough people are available for scheduled trials without bringing them all to the jury room to wait.
TL;DR (Too Long; Didn't Read)
The standby system of jury duty requires that people called to serve check in by phone rather than showing up at the courthouse in the morning. They only have to go in if and when they are needed.
An Inconvenient Necessity
For many people, jury duty is an inconvenient necessity, or at least it used to be. Obviously, being tried by a jury of one's peers is a democratic right, and to make that work, people from all walks of life must serve. But jurors have to miss work, travel to courthouses across town, arrive on time and then wait. Although your employer must allow someone to serve and continue to pay them, it's a nuisance, especially if they are never selected to hear at case.
The Jury Duty Standby System
The standby system was intended to ride to the rescue by eliminating some of the inconvenience. If someone is called to jury duty, they check in by telephone to find out their instructions. For example, if they are called to serve on Monday morning at 8 a.m., they can call Friday and listen to the recorded message telling them whether and when to show up, or when to call back.
They may be told to report Monday at 8:00 a.m., to check back at noon to see if they are needed for the afternoon or simply to call in later to see if they should show up Tuesday. In the meanwhile, they can report to work. They must keep checking back until they are either told to report to the courthouse or that their service is complete without having to report.
Variations on Standby Rules
Not all standby rules are the same, so if someone is called for jury duty, they can read up on how it works in their jurisdiction. It varies even among counties in the same state.
For example, in some counties in California, like San Diego, every juror begins service on standby status. In other counties, like San Francisco, each potential juror is assigned to a group, and some groups of jurors are on standby and some are not. Those that are not must show up at the courthouse.
In Cook County, Illinois, jury duty notice will specify if someone is on standby. If they are, they call in. If the notice does not mention standby, they must show up at the court.
Ignoring the Jury Summons
It's neither very responsible nor very wise to ignore a jury notice. The trial court system of the United States depends on people appearing when summoned as potential jurors. And those who ignore the notice and fail to respond or appear will probably regret it.
Usually, the judge in charge issues a bench warrant for their arrest. That means that if they are stopped by the police for some small infraction, like a broken brake light, they will be arrested and taken before the court.