In addition to recoding video, another great security method is to record audio. This is perfect for retail where you want to record the audio of a number of different situations that might occur. Once the audio is recorded then you can watch back the video with the matching audio. In order to record audio you first need to make sure that your DVR can record audio. Most DVRs record at lease one audio channel. The second step is to connect a powered microphone to your DVR and install it where you want to record the audio.
You can view more information on Powered Microphones here