DENVER — After another school shooting in Colorado last week, many parents and students are rallying schools to install metal detectors.

Several parents created a petition demanding better security measures at all schools, including metal detectors.

RELATED: Douglas County sheriff pulled SRO out of STEM School last year in pay, performance dispute

RELATED: 1 student killed, 8 others injured when classmates open fire at STEM School Highlands Ranch

But some school safety experts warn metal detectors aren’t that simple of a solution.

“I think there are better ways to spend resources than metal detectors,” said Christine Harms, director of the Colorado School Safety Resource Center.

Harms said research is not conclusive as to whether or not they are helpful or even effective in stopping school shootings. And, she says, metal detectors are expensive to purchase and staff.

She also says they can have an unintended impact.

 “The fear also is that school won’t feel like their school is a warm welcoming place when they feel it’s more like a prison,” she said.

A week ago, two students entered STEM School Highlands Ranch, armed with handguns and a rifle in a guitar case.  Many parents argue if the school had had metal detectors, those students would have been caught.

First responders at STEM School

“I can understand the knee-jerk reaction that metal detectors may have worked in this kind of case, but overall speaking, there have been situations where schools had metal detectors and students still got in with a gun,” Harms said.

So how would harms better spend funding for school safety? Door locks.

“To my knowledge we have not lost any students in an active shooter situation in the United States when they are secured behind a locked door,” Harms said.

RELATED: 'A guitar case with guns made it into the school': DougCo commissioners allocate $10M toward school safety

Many schools in Colorado have hardened classrooms by adding or improving upon door locks. But Harms said there are still more to go.

In 2018, state legislators allotted $29.5 million for school safety improvement grants for schools.

“Some of the things that schools asked for were things like classroom locks on doors,” Harms said.

Other schools needed improved locks on classroom doors.

In all, Harms office received $60 million in requests for grants, many from rural school districts with fewer resources and bigger safety needs.

“One of the grants was asking for new front doors because they literally couldn’t lock the front doors of their school building,” she said.

Harms also said schools need to invest in less visible safety measures.

“I’d like us to be very thoughtful of how we’re going to spend any resources when it comes to school safety because it’s not only physical security we have to consider but it’s also psychological safety,” she said.

“If a student feels a connection to the school and feels like there’s an adult, at least one, that they feel close to, they have peers there, they are much less likely to act in any violent way towards the school,” she said.

RELATED: Celebration of life for Kendrick Castillo will be held Wednesday

RELATED: Student killed at STEM School Highlands Ranch lunged at gunman, classmate says 

SUGGESTED VIDEOS: Next with Kyle Clark