What is T1 in this circuit for 'Mains power failure alarm'?
A little bit of googling would have helped here.

Here is the main page for the design: http://www.circuitstoday.com/mains-failure-alarm-circuit

And the relevant component choice notes:


T1  can be  a 230V primary   6V secondary  500mA  transformer.
B1 can be a 1A bridge.You can make the same using four 1N 4007 diodes.
All capacitors are rated 25V. 
You can use any general purpose PNP transistor (like BC158,BC177 
etc) as Q1.