LOS ANGELES (CBSLA) — Lori Meisenheimer and Dana Cipolla are friends from Newport Beach who both received threatening robocalls claiming to come from IRS headquarters.

They know better than to answer unrecognizable numbers, but they’re nervous they’ll miss answering legitimate ones if they don’t pick up.

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“I have pharmacies and doctors that do robocalling, and so those I need to answer,” Cipolla said.

There are several apps that block pesky robocallers. YouMail is one of them. It’s a free service based out of Irvine that tricks robocallers into thinking you don’t exist.

YouMail works by playing an out-of-service message to any number it recognizes as a bad number.

YouMail CEO Alex Quilici says that at first, the robocall-blocking feature was an accident.

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“Originally, we had a feature that would play the out of service message to your ex-girlfriend or your ex-boyfriend, and we recognized that people were using it to block telemarketers and all sorts of numbers. We realized we could help people by doing that automatically,” he said.

YouMail’s fingerprinting technology recognizes robocallers’ voicemails and cross-references them to its library of bad numbers.

Here’s what you can do to avoid robocalls:

  • Never answer unknown phone numbers
  • Get a robocall blocking app on your cellphone
  • If you answer, never press the number they claim takes you off their list.

If you’re unsure of an unknown number, check it out on google or type it in at youmail.com.

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And f you were wondering, YouMail is able to offer the robocall-blocking service for free because it makes its money offering voicemail services to businesses.