Yes, life insurance companies will know if you smoke.

If you purchase a life insurance policy they ask you on the application form about any tobacco use. If you answer "yes", you do smoke, they will know. Also, some insurers require you to take a blood test and medical exam which will determine if you smoke.

However, there are life insurance companies that offer life insurance without any medical exams or blood testing.

But make sure you do not lie on the application for life insurance because that would open up the chance of a claim on your life insurance policy being denied due to misrepresentation of a material fact when you applied for the life insurance.

Here's how you may qualify to buy life insurance without any medical examination required.