I wanted to know how can i make a voice activated door lock using arduino uno as part of my project.
Without dedicated IC to deal with the voice processing part, it's unlikely that you'll go far with the Arduino alone on this project. The Arduino simply doesn't have the necessary processing power to do sound processing.
You might be able to buid a clap activated lock though. By using something like this connected to the arduino’s analg pins, you would be able to detect a voltage spike, caused by someone clapping. You can then control the lock. As Korman said though, an arduino wouldn’t be able to process speech.
Someone posted in exhibitions a project that used pattern recognition. You could do something similar, perhaps enter a morse code type pattern on a silent button so your neighbors couldn't hear you tapping out ... - - - ... to get in.