A UPS is an uninterruptible power supply that protects equipment from power outages and network fluctuations and allows for safe completion of work or controlled shutdown of the system. The basic modes are offline, line interactive and online, which differ in quality of stabilization, switching time and degree of isolation from the grid. Important features include AVR automatic voltage regulation, surge protection, noise filtering, fast battery switchover and deep discharge protection. Advanced models offer communication via USB or network interface, remote monitoring, self-testing of batteries, off-grid cold start and smart charging for longer battery life. Active power in watts, apparent power in volt-amps, power factor, backup time and type of connected load are monitored for proper selection. A properly selected UPS increases system availability, protects data and reduces costs associated with power outages and failures.