music source to awaken the sleeper. Some models come with a dock for iPod/iPhone that also charges the device while it is docked. They can play AM/FM radio, iPod/iPhone or CD like a typical music player as well (without being triggered by the alarm function). A few popular models offer "nature sounds" like rain, forest, wind, sea, waterfall etc., in place of the buzzer. Clock radios are powered by AC power from the wall socket. In the event of a power interruption, older electronic digital models used to reset the time to midnight (00:00) and lose alarm settings. This would cause failure to trigger the alarm even if the power is restored, such as in Home Alone 2: Lost in New York. Many newer clock radios feature a battery backup to maintain the time and alarm settings. Some advanced radio clocks (not to be confused with clocks with AM/FM radios) have a feature which sets the time automatically using signals from atomic clock-synced time signal radio stations such as WWV, making the clock accurate and immune to time reset due to power interruptions. Alarms in technology Computer alarms Alarm clock software programs have been developed for personal computers. There are Web-based alarm clocks, some of which may allow a virtually unlimited number of alarm times (i.e. Personal information manager) and personalized tones. However, unlike mobile phone alarms, they have some limitations. They do not work when the computer is shut off or in sleep mode. Mobile phone alarms Many modern mobile phones feature built-in alarm clocks that do not need the phone to be switched on for the alarm to ring off. Some of these mobile phones feature the ability for the user to set the alarm's ringtone, and in some cases music can be downloaded to the phone and then chosen to play for waking. Next-generation alarms Scientific studies on sleep having shown that sleep stage at awakening is an important factor in amplifying sleep inertia. Alarm clocks involving sleep stage monitoring appeared on the market in 2005. The alarm clocks use sensing technologies such as EEG electrodes and accelerometers to wake people from sleep. Dawn simulators are another technology meant to mediate these effects. Sleepers can become accustomed to the sound of their alarm clock if it has been used for a period of time, making it less effective. Due to progressive alarm clocks' complex waking procedure, they