The Supernaturalist by Eoin Colfer. The plot summary from Goodreads goes:
In the future, in a place called Satelite City, fourteen-year-old Cosmo Hill enters the world, unwanted by his parents. He's sent to the Clarissa Frayne Institute for Parentally Challenged Boys, Freight class. At Clarissa Frayne, the boys are put to work by the state, testing highly dangerous products. At the end of most days, they are covered with burns, bruises, and sores. Cosmo realizes that if he doesn't escape, he will die at this so-called orphanage. When the moment finally comes, Cosmo seizes his chance and breaks out with the help of the Supernaturalists, a motley crew of kids who all have the same special ability as Cosmo-they can see supernatural Parasites, creatures that feed on the life force of humans. The Supernaturalists patrol the city at night, hunting the Parasites in hopes of saving what's left of humanity in Satellite City. Or so they think. The Supernaturalist soon find themselves caught in a web far more complicated than they'd imagined, when they discover a horrifying secret that will force them to question everything they believe in. Eoin Colfer has created an eerie and captivating world-part Blade Runner, part futuristic Dickens-replete with non-stop action.
I've read the book several times, and I promise you it hits all the beats:
Protagonist exposed to product testing
Satellite City was not part of any welfare state, so its institutions had to raise funds in any way they could. Clarrisa Frayne's [the orphanage our protagonist belongs to] speciality was product testing. Whenever a new food or untested pharmaceutical product was being developed, the orphanages volunteered it's "no-sponsor" charges as guinea pigs.
The no-sponsors relaxed once Redwood [the Marshal] had gone, and the silence of discipline was replaced by the groans and sobs of boys in pain. Cosmo [our protagonist] touched his legs gingerly where a particularly acidic spray had actually burned the skin.
Climb a ladder into bed
Three hundred orphans turned immediately to the dozen or so steel ladders, and began climbing. Nobody wanted to be stranded on the dorm floor once the ladders were retracted. If the marshals caught a no-sponsor on the ground after lights out, a ten-mile run would seem like a Sunday stroll compared to the punishment they would dish out.
Cosmo climbed quickly, ignoring the pain in his leg muscles. His pipe was near the top. If the lights went out before he reached it, he could be stranded on the ladder.
The protagonist escapes. I can't find a convenient quote for this (the escape covers most of a chapter), but I assure you it happens.
The protagonist can see invisible monsters most people can't, and he runs into a group of kids who can all see them
"We, Cosmo Hill, are the world's only Supernaturalists."
"We call ourselves Supernaturalists because we hunt supernatural creatures."
"There aren't many of us [who can see the creatures]," said Stefan, looking Cosmo straight in the eyes. Cosmo made an effort not to look away. "Not enough to be believed. It doesn't help that most Spotters are kids. Maybe our minds are more open."
The protagonist joins the group and fights monsters
"You're a rarity, Cosmo. Your choice is to be a rarity with [the Supernaturalists], where it will do some good, or go back to Clarissa Frayne."
What choice? Cosmo would take his chances with a thousand Parasites before returning to the orphanage. A person can only take so many medical experiments.
"I'd like to stay."