Most life insurance policies will pay out on death regardless of how you die, as long as there are no discrepancies in the medical information you submitted to the life insurance company when you set the policy up. However, there are some policies that only pay out in the event of your death being the result of an accident.
These 'accidental death' policies can seem to be quite cheap and are normally sold by banks and building societies. Sometimes they are even provided free for the first few months as a 'reward' for setting up a new account or credit card. After the first few months, you will normally be expected to pay the premium yourself and because these plans provide very restricted cover and the premiums are often quite small, many people do just that, sometimes without even realising it.
However, these are not full blown life insurance plans as they will only pay out the full sum assured if you die as a result of an accident and not natural causes such as a heart attack or cancer. For this reason you are likely to be better off investigating a more comprehensive life insurance plan instead of a restricted 'accidental death' policy.
Some normal life insurance plans offer an additional sum assured that can be taken out to cover accidental death where the amount payable is increased because of the fact that the person covered died as a result of an accident. However, this is probably not a reason to chose one policy over another as the important thing is to make sure that the person whose life is being covered has the correct amount in place, regardless of the way the way they die!