You see them all over Pinterest, Etsy, and in stores: Car seat accessories that claim to solve a number ofproblems that arise when transporting small children, like entertaining them, making them comfy while they sleep, or keeping them cool. But are they safe?

I spoke with car seat safety expert Jennifer Johnson, BNS, RN, and CPST, who is also a nurse at Parkland Hospital in Dallas, Texas, about some popular car seat accessories I have seen both in stores and online. She has a three-year-old son, so car seats are a big part of her daily life, but so are daily struggles with getting in the car and staying there for long rides.

“Before really looking at any of them, I’ll give you this: If it didn’t come in the box, it shouldn’t be on the seat,” says Johnson. “That includes seat covers made at home or by anyone other than the manufacturer of the car seat, as well as those toys that people put on car seat handles.” Remember, products have to be proven dangerous to be recalled, so just being available in stores or online is not an indication that it’s been vetted for safety. An item will not be recalled until it injures or kills someone.

With that in mind, we reviewed some popular accessories from around the web.

Slumber Sling: This is a momma-made headstrap that goes across the car seat to keep baby’s head upright when sleeping. “This item makes me wonder how many babies/toddlers will be choked when it slips down and goes around the kid’s neck.”

Backseat Mirror: These mirrors vary from models that hang over the headrest to ones that strap on so mom can always see a rear-facing baby. It matters how it’s attached, says Johnson. “The backseat mirrors can come loose and become a projectile in a wreck.”

The Noggle: The Noggle is a long air-vent extension that snakes into the backseat to help heat or cool rear-facing kids.  “The Noggle is good in theory, because the back seat can get hot, especially in the summer in a hot area with a rear-facing baby or toddler. But it’s basically another projectile–a giant one.”

Seatbelt Pillows: These are basically oblong pillows that wrap around the seatbelt to give kids a place to rest their heads when they fall asleep. “Pillows for the seat belt or the belt positioners can keep the belt from tightening the way it needs to in a crash, which then prevents the belt from working the way it needs to in a crash, and can cause injury to the child or can allow them to slip out of the belt and be ejected from the vehicle.”

Seatback Organizers: These hook over the seat in front of baby to store things like diapers, toys, wipes, and other diaper bag essentials that end up in the floor. “The organizers can hit a front-facing child and cause injury. The stuff that’s jammed into them can become a projectile as well. It’s not just the weight of the thing itself; it’s the weight times the acceleration of the vehicle and the force that creates that hits the baby. An empty soda can could crush a human skull at the right velocity.”

And that comment brings us to the most important part of car safety, and probably the hardest one for any mom: keeping your car clean. “It’s hard to keep your car clean with kids in it. I know that! But it’s really important,” says Johnson. “In general, you should have the least amount of crap in your car as possible, and whatever isn’t attached to the car needs to be secured: purses, toys, seatbelts not in use need to be buckled, even if there is a car seat in that seating position.”

If you are in an accident, paramedics and emergency personnel will use your child’s car seat to transport them in the ambulance, too, says Johnson, so make sure your car seat has a sticker with your emergency information on it. “I recommend that parents put the child’s name, birthdate, and parent’s emergency contact info and any allergies/health conditions, in the event that there’s a wreck and the child has to be transported to a different hospital than the parent(s).”

You can download a free printable car seat emergency sticker like the one shown here.

Erin Burt is a freelance writer and mother of three girls who lives and writes in Queensbury, New York.