ISD1820 Voice Recording Module is another very interesting stuff. You don't need to prepare a speaker and a mic - both are included in this module! After connecting to the power, you can press REC to record a 10 second voice. Press PLAYE to play the complete voice once. Press and hold PLAYL it will play the voice and it stop when the button is released. It can also be controlled by Arduino. Combined with Laser Detector and Laser Module, you can make a doorbell, security system, and power-saving light along corridor for instance.