VTech’s Power Fail back up system lets you make calls during a mains power interruption with your cordless phone. During a mains power interruption you can supply the power stored in your handset battery to the base unit, so you can make calls even when the power is out. Advanced Dual Antenna System for extended range. SOS help button on handset with user pre recordable alert message. Calling Number Display Call Guard allows you to block unwanted PRIVATE and/or UNAVAILABLE calls plus the Call Block List which allows you to block incoming calls from up to 50 specific user programmable numbers.