A lot of people use bikes these days, it's way easier to travel within the city and you can avoid traffic. Quite a few of these bike owners have come back to their bike parking spot to see that their bike is no longer there, stealing bikes is quite easy without the right lock. There are quite a few of these bike locks being sold in malls and such but only a few of them can actually protect your bike which is not good. Make sure that you have a durable and reliable heavy duty bike lock to protect your bike, this is the only way you can protect your bike in a bike theft area. If you are in a minimal crime area, a think cable lock can be sufficient in protecting your bike.
These thin cable locks will not work against bolt cutters though, the common tool used by thieves in crime filled areas. But this is a good choice for preventing casual types of stealing like someone walking by and decides to borrow your bike for a while. In a place where theft is prone, you should go for the steel U-lock which is durable and is also the most recommended type of heavy duty bike lock around, you put ir around the frame of your bike and the front tire and a strong, stationary object like a fence or an electric pole. By bringing an extra U-lock, this will help you from extreme theft areas which will lock down the rear wheel, making it even harder for the thief to ride away with your bike. You can just put some additional cable or even better, take the bike with you if you do not want it to be stolen.
Your bike seat can be stolen as well, that is why you should think about locking that down with cable. Or you can have it changed with a piece that will need an allen wrench to be removed in order to avoid having your seat stolen together with your chained down bike. But you have to know that a good bike lock is not that cheap. But if you think about it, a stolen bike is way more expensive than buying a good bike lock. Ask around the place to know about the current situation with bike thefts. The best place where you can get valuable information will be at the local bike shop where the owner will surely know how many owners went back to buy a new bike. Know more facts about bike lock at https://www.huffingtonpost.com/2012/09/24/canned-air-bike-locks-video_n_1911124.html.
To protect your bike, make sure you know the current situation so that you can buy the necessary precautions to protect your bike from thieves.