Useful information about preventing basement flooding with sewer backwater valves, including photos and videos on how different types work to protect.

Backwater valves, also known as check valves or sewer backflow prevention devices, reduces or eliminates sewage backups into your basement when stormwater surges into the sewer system during heavy rainfalls. They work by allowing water to flow in only one direction. There is a flap or some other device that will allow water to leave your home, but will close shut when sewage from the street puts pressure into your discharge pipes. Here is a short video showing how they work.

Some things to know about backwater valves...

They require regular inspection and cleaning, about once a year.
Some types will not stop 100% of the sewage but will stop most of it. I've heard people reporting they now have a small puddle to clean up instead of several inches of sewage.
When activated, you should stop using the drains inside the house. The device will be shut and the water won't be able to exit your home.
They need professional installation. Special attention must be paid to how your gutters and sump pump discharges.
They can be intrusive to install. They require either digging up part of your basement or your front yard.
Cheaper plug types can work in some cases, but are not recommended because they allow pressure to build up inside your basement floor and can cause structural damage.
They can be expensive, in the range of $1,500 to $10,000. The cost depends on a variety of factors based on your specific plumbing setup.
The City of Berkley will refund permit fees related to their installation.
Oakland County has a Home Improvement Program that can help qualified homeowners to pay for this expense.

Despite the long list of things to consider, many people I know who have installed them have reduced or eliminated their basement flooding and are much less anxious about large storms.