Beginning in Los Angeles, Wheels will mount helmets on the rear fenders of its bikes that can be unlocked and worn during a trip, then reattached to the bike. The helmets will have removable liners, Wheels said in a blog post.

The Wheels helmet, as well as an earlier program by rival scooter rental company Bird to give away 75,000 helmets, comes as public health experts and regulators are sounding alarms about the safety of electric bikes and scooters.

Policy makers in cities from Singapore to Paris to San Francisco have begun hitting the brakes on e-scooters, banning them from sidewalks or restricting where and when they can be used.

Wheels riders who unlock the helmet will get a 20% discount on the cost of their trip. Sensors in the bike can detect when the helmet is returned, the company said.

Wheels cited in its blog post a recent UCLA study that found head injuries sustained by riders who were not wearing helmets were the most common injuries among 249 people admitted to emergency rooms after electric scooter accidents in California.

A study by the U.S. Centers for Disease Control and Prevention and the public health department of Austin, Texas, logged 190 injuries among electric scooter riders between Sept. 5 and Nov. 30, 2018, of which 48% were head injuries.

Investors have poured money into e-scooter and electric bike-sharing companies in recent years, chasing mainly urban dwellers seeking an alternative to walking or taking a car or public transit for relatively short journeys. Boston Consulting Group earlier this year reported that a dozen electric scooter companies had raised $1.5 billion from investors.

Wheels said in October it had raised $50 million in a funding round led by DBL Partners.