Does the money come from your parents? If so, they have the right to snoop into your check book. Also, even if the money is yours, if they are paying for your car or college bills, they have some right to know how you are spending your money while they are supporting you, as you shouldn't be living it up while they go through financial hardships to help you out.
If they are not supporting you, and the money is yours, you should buy a fire proof metal security box, with a lock, and keep any private papers, including your check book in there. Also, it is not a good idea to carry your check book around with you. If someone were to steal your wallet/purse, they would be able to use your checks. Only carry your check book when you know you will need to use it away from home. The rest of the time use cash or a debit or credit card.
Bear in mind, if you are still living with your parents, they may object to your having a locked security box that they can't get into. This is because young people sometimes get into drugs, illicit sex, gambling, and other bad things, and parents have a responsibility to try to keep that from happening. And, if it does happen, they have to try to save their child from the child's own bad choices. To do this, parents need to know what's going on, including whether there are any drugs, birth control pills, or other things in the child's possession. That means no locked hiding places that the parents can't get into.
If you are still living at home and want more privacy, you will have to find a way to move out.
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If a man does not keep pace with his companions, perhaps it is because he hears a different drummer.
Let him step to the music which he hears, however measured, or far away.--Henry David Thoreau