Drug experts had a stark warning for worried parents who gathered in the auditorium of Park City High School to learn about teen addiction: Knowing the signs is not enough.

Even in the state's most privileged school district, law enforcement officers said, parents have to convince themselves that their kids are vulnerable.

"Please don’t turn a blind eye and think, 'Aw, it’s not going to happen to me,'" said Summit County Sheriff's Lt. Greg Winterton. "... Drugs have no boundaries: rich, poor, in between."

Scores of parents turned out Monday night for a community meeting on how teens may use the internet to obtain illegal drugs, and how parents can tell whether their children are using. The meeting came just three days after a Park City family sued the companies that they say facilitated the delivery of synthetic opioids to their 13-year-old son, who died in an overdose.

Two days after Grant Seaver’s death in 2016, his friend, Ryan Ainsworth, also 13, died after ingesting the same drug, called “pink.” A group of teens bought the drugs through the darknet, a restricted-access and covert internet network.

The darknet, or dark web, and its parts — browsers, markets, currency — are not inherently bad, explained Clint Kehr, a Washington, D.C.-based agent with the U.S. Bureau of Alcohol, Tobacco and Firearms; dissidents in repressive political regimes use the dark web to circumvent state firewalls, for example.

But it also poses a host of new challenges to parents who may not even recognize the array of app icons that might pop up on their kids' phones — much less know whether they are being used for dangerous purposes, Kehr said.

"Kids are smarter than us when it comes to technology," said Beth Cummings, a Park City parent with children in middle school and elementary school.

When Kehr asked how many of the parents in Monday night's crowd had ever been on the dark web, only a handful raised their hands.

Kehr opened his projected computer screen to a Youtube video on how to use Tails, an encrypted operating system often used to access the Dark Web.

"I can tell you your kids are watching this and learning how to use Tails," Kehr said. "... You have to do research. Your kids are doing research."

To monitor kids' dark web activity — especially any elicit purchases — parents should be familiar with cryptocurrency like Bitcoin and learn to recognize signs it's being used. A nonsensical sentence may be a passcode. A long string of numbers and letters might be a Bitcoin address.

"If your kid has this written down, you might want to ask them how they’re doing on their Bitcoin investments," Kehr said, demonstrating how to sign into Blockchain — a ledger of transactions.

Markets like Dream Market connect sellers and buyers, who can arrange drug purchases. Like on eBay, sellers are rated for service and for product quality. "Stealth was good," writes one reviewer of a cocaine merchant — meaning the drugs were well-hidden in their package.

Logos for apps on kids' devices can reveal dark web use, Kerh said, displaying a tableau of icons for apps like Orbot, Orfox, Fire onion, Coinbase, Bitcoin Wallet, Red Onion, and the Tor browser.

"See if your kids have these installed on [their] phone," Kehr said. "Ask them why. 'Why do you have this?'"

But also know that, for example, the Tor browser icon can be replaced.

"It’s built to get around oppressive regimes. Or oppressive parents," he said.

A closer look at a child's digital activity may start with signs of drug use, Winterton said. A surge of hyperactivity, aggression or sleepless nights might indicate meth use, but combined with physical signs, like scabs from skin-picking, dilated pupils, or weight loss, a parent should become all but certain.

For opioids or opiates, look for constricted pupils — "I mean pinpoint," Winterton said — and signs of itching, nausea, vomiting or constipation. A recent switch to long-sleeve shirts, no matter the weather, can mean injection marks are being hidden. A recent surgery or injury can be another clue; most teens Winterton encounters became addicted as a result of a valid prescription.

Further investigation may feel invasive, but do it anyway, Winterton said. Resist the urge to stop with a cursory glance around a bedroom, he said; look through a child's belongings — backpacks, pillowcases, pockets, any other hiding places. Examine their body for injection marks, Winterton said.

“Check their arms, check between their fingers, check between their toes, check their eyelids. These kids will inject this stuff … any way feasible. That’s how addiction is,” Winterton said. “If you have a totality of [clues], and you think you have a sign, check. Is it going to piss them off? Absolutely. Is it worth it? Absolutely.”

The parents of a Park City teenager who died in 2016 from overdosing on a synthetic opioid are suing the companies that helped bring the drugs from China into Utah.

The lawsuit, filed Friday in Utah’s U.S. District Court, argues the now-defunct online darknet (a restricted access and covert Internet network) market AlphaBay and the estate of its deceased founder, Alexandre Cazes, in addition to The Onion Router (or TOR) darknet web browser and China Postal Express & Logistics, a postal service, are liable for 13-year-old Grant Seaver’s death. Seaver’s friend Ryan Ainsworth, also 13, died within two days of Seaver in September 2016 after they both ingested the synthetic drug, called “pink,” “pinky” and “U-47700.”

Seaver’s parents, James and Deborah, have already sued Ainsworth’s parents, in addition to the parents of another teenage boy and a 17-year-old girl who was criminally charged in July for allegedly ordering more drugs from the internet to be shipped to her. That lawsuit alleges the parents knew their children were ordering drugs off the web and sharing them with friends, but they didn’t report the behavior to police.