During the original airing of this NBC Charlotte investigation, we inadvertently aired video of a security company that was not part of the investigative report. We apologize for this error and any confusion it may have caused.

You may be safe in your own home, but there's still a lot that can go wrong. That's why most of us now have security systems: To wake us when there's a fire or call the police when an intruder breaks in.

The Defenders finds those systems may not always be so reliable, giving you a false sense of security at the very worst moment.

Kim Connor knows what it means to be homeless, but it wasn't always that way.

Once, she owned a 1930s style barn home. It was even featured on a home renovation show called 'Rezoned'.

"I miss it terribly. I spent eight years renovating it and it was my dream home," said Connor, who lives in Jamesport, Missouri.

Which is why she wanted security and got a fire and burglary system from ADT, one of the largest and best-known home security firms in the country. But one night, her special house caught fire and burned to the ground..

Connor said the alarm system didn't go off until she had already left the house. She had a backup smoke detector installed years earlier, and she says it probably saved her life.

"Even a few more minutes and I probably wouldn't have been able to get out," said Connor.

But worse, it never contacted the fire department the way it was supposed to. Something ADT denied responsibility for in a letter to her.

"Why am I giving you my money, trusting you with my life and property?" said Connor of her eight-year history with ADT. Connor had insurance but says it didn't cover a fraction of her home's value.

ADT told us in a statement, “While ADT sympathizes with our former customer, please keep in mind alarm systems don’t start fires and cannot prevent them from occurring.”

But it's a question others have asked.

In fact, across the country, Five On Your Side discovered lawsuits filed against ADT making similar claims.

Some of them tragic.

Like a suit involving Teri Lee, a Minnesota mother who was being stalked by an ex-boyfriend. She had an ADT system installed at her home but not long after, the boyfriend broke in and murdered her.

Her family's lawsuit claims that the ADT system never alerted her and that some alarm sensors failed. ADT eventually settled the case.

But what's going here?

Home security expert Chris Robertson with Assurance Protection said part of the problem is that ADT sells franchises to private companies that in turn sell the service to you.

"Sometimes you're dealing with authorized dealers that have no direct affiliation with ADT. They seem to run freely and operate at their own pace with very little oversight," said Robertson.

And that includes the quality of the subcontractors that they hire to install your system.

"There's a breakdown sometimes when that happens," said Robertson.

In response, an ADT Spokesman told us in a statement, "ADT along with its Authorized Dealers have earned the highest ranking (A+) from the Better Business Bureau for delivering excellent customer service.”

But sometimes, it's improved technology that's the problem.

"The right equipment and the right device will give us access to just about anything in this house," said Mike Barberi, Security Expert who showed us more alarm system vulnerabilities brought up in a class action lawsuit against ADT.

The vulnerabilities? Hackers infiltrating the security system.

With a simple frequency analyzer, a hacker could not only gain access to your home's security system but be able to monitor everything that goes on inside your residence.

But even worse, they can turn off the system. Barbieri said although the class action is filed against ADT, any alarm system can be infiltrated this way.

ADT declined to comment on the recent litigation surrounding its systems security.

Which brings us back to Connor. She eventually built another home right on top to the home she lost and said she'll never trust any alarm company to help her sleep well at night again.

"There's a good chance it might not function when they need it or function correctly and it can be life-changing. It certainly changed my life," said Connor.