This walkthrough explains how to find and use the Biosensor Scope (infrared sight) in the Resident Evil 4 remake.
Despite all the new features in the Resident Evil 4 remake, one thing remains the same: Regeneradors are impossible to kill—unless Leon has a thermal vision device, the Biosensor Scope. As the name suggests, the Biosensor Scope is an infrared sight mounted on rifles and some SMGs. It detects all entities emitting heat while exposing the Plagas inside the Regeneradors and Iron Maidens.
In the original Resident Evil 4, Leon could obtain the thermal scope at the Freezer of the Lab, where he first comes across the Regeneradors. This hasn’t changed in the remake, and he still needs to look for it in the Lab. But thanks to the revamped—and more complicated—puzzles, it’s easier for him to miss it. To help with that, this guide shows the Biosensor’s exact location and explains how to use it effectively.
Although the remake calls it a Biosensor (not an Infrared Scope), the functionality is unchanged. Once attached to a scope-compatible weapon, the sight shows the hot and cold spots of organisms, with reds signifying the hottest and dark blues the coldest.
How to Get the Biosensor Scope
After solving all Electronic Lock Terminal puzzles in the Lab, enter the Incubation section, and grab the Biosensor Scope sitting on the desk. A gem icon marks the scope for players who’ve bought the treasure map of Chapter 13.
Players do not need to solve any puzzle to get the Biosensor Scope. But getting into the Incubation Lab—where the scope is kept—requires a level 3 key card. Here’s a step-by-step guide for that.
- Start with switching power to the Dissection room.
- Solve the Dissection door puzzle.
- Grab the level 1 key card in the Dissection.
- Switch the power to the Freezer.
- Put the level 1 key card in the overwrite device.
- Grab the level 2 card and leave.
- Use the level 2 card to enter the Incubation section.
- Get the Biosensor Scope in the Incubation Lab’s control room, the one that prompts Leon to find the wrench.
Tip:
Do not shoot the Regeneradors’ holding tanks before getting the Biosensor Scope. Otherwise, they will all break out and attack.
How to Use the Biosensor Scope
Hover over the Biosensor Scope in the inventory and press A (X on PlayStation). Select “Parts” and attach the sight to any scope-friendly weapons, the CQBR assault rifle, Stingray, SR M1903, or LE 5. The scope automatically activates a thermal or infrared vision, enabling players to see heat sources.
Ideally, players should use the Biosensor Scope to locate and shoot the Regeneradors’ parasites. Under the infrared vision, these creatures are seen as shiny, red, heart-like entities.
Note:
The only way to switch the Biosensor off is by detaching it.
The Best Weapon for the Infrared Scope
The Biosensor Scope’s primary function is to reveal parasites inside Regeneradors. With that in mind, players would benefit from it the most when mounted on rapid-fire weapons like LE 5. Because it takes at least three accurate shots to kill a Regenerador, players need a gun with a fast rate of fire, so they have enough room to miss a few. And LE 5 is just that.
With a Biosensor-attached LE 5, players can shoot simultaneously at the proximate location of all three or four Plagas, giving the Regeneradors no chance to react. (The LE 5’s low power is not a concern because the parasites are weak; they die with one bullet of any caliber.)
Other Uses of the Biosensor Scope
Because infrared vision exposes all heat-emitting entities, it can be used for spotting disguised enemies like Novistadors, sniping Araña-type Plagas, and hunting black basses in the dark. But it’s generally not a necessary attachment in Regenerador-free chapters.
The Resident Evil 4 remake is available now for PC, PlayStation 4, PlayStation 5, and Xbox Series X/S.
