How can you get Free Money?

There is a giant stereo system on the lower left area of your base that has a 'Play' button on it. If you tap on it it will begin to play loud music that will attract a horde of zombies towards it. When this happens your troops will open fire on them from the saftey of behind the fence.

Any zombies that get slain while the loud music is playing will drop money and after your troops have finished dispatching them a crate will appear above the stereo that will be full of money. To add the money to your total you must first tap on the crate and then go to your inventory in order to claim the money.

Each time you have used the stereo there will be a few minutes where it will go on cooldown before you can use it again. Play the stereo whenever possible so you get as much money from it as possible.