If you had friends or family in Paris over the weekend, you might have been notified by Facebook that they were "safe" – and they may have been kept safe with free rides from Uber, free shelter through Airbnb and free taxi rides citywide.

Within 24 hours, Facebook helped four million people in Paris use its "Safety Check" feature to let family and friends know they were safe. Originally developed for natural disasters, this was the first time the tech company activated the feature for a terrorist attack.

The video below shows how it works.

After its activation by company officials, people in the danger zone receive a message from Facebook asking if they are safe. They then click one of two buttons — one saying they are safe or one saying they are not in the area — which shows up as a message to friends.

Ride service, Uber, quickly switched off surge pricing – the higher fees that automatically kick in when demand rises. The company quickly realized what was happening and disabled the feature in Paris. Their app displayed a message asking users to shelter in place until a ride arrived, and many drivers reportedly offered free rides.

Within 24 hours, Facebook helped four million people in Paris use its "Safety Check" feature to let family and friends know they were safe. Originally developed for natural disasters, this was the first time the tech company activated the feature for a terrorist attack.

The video below shows how it works.

After its activation by company officials, people in the danger zone receive a message from Facebook asking if they are safe. They then click one of two buttons — one saying they are safe or one saying they are not in the area — which shows up as a message to friends.

Ride service, Uber, quickly switched off surge pricing – the higher fees that automatically kick in when demand rises. The company quickly realized what was happening and disabled the feature in Paris. Their app displayed a message asking users to shelter in place until a ride arrived, and many drivers reportedly offered free rides.

At the same time, Parisian taxis were living up to their patriotic heritage. Famous for once saving the city by driving soldiers to the front and thwarting a World War I German advance on the City of Light, cabbies drove people away from danger Friday.

They offered free rides to people near the scenes of the multiple attacks. People were able to summon them with a "Le Taxi" app, rolled out less than a month earlier.

Airbnb, the home-renting service, joined Twitter in the #PourteOuverte (open door) campaign to find visitors temporary housing during the crisis. The hashtag allowed Twitter users to let others know they were offering a room for people needing a place to stay.

Airbnb immediately waived all service fees for people checking in to Paris accommodations between November 13-17. Then went even farther, asking its members and hosts in an email to open their homes (pictured above).

"If you are able, we hope you will strongly consider helping those who are in need by making your listing available at little or no cost," the company's message read. "Also, if you're an Airbnb host in Paris and your Airbnb guest is experiencing travel delays as they try to leave Paris, you can allow your guest to extend their stay for free."

Use The Same Tech To Share This Story… (Photos: Hernán Piñera, CC; Facebook; Airbnb)