A friend said their new 2018 Corolla starting making weird alarm-like noises during a drive, apparently b/c they were driving too close to another car in front of them. I took a look at the front end of the car to figure out how it works. I could see something that looked like a diode laser attached to the lower radiator area, and pointing forward so it was aiming through a portion of the front grill. Is that how it works, just a single laser? I Googled Toyota’s website expecting to see it uses radar, but it suggests there’s just a camera and a laser. I couldn’t see any camera. Just what appeared to be a laser. Anybody know how it works? And where those anti-collision gadgets are located on the car?
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From what I can glean it is a laser. Police have been using laser with or instead of radar for a long time to catch speeders. Much tighter beam, easier to focus on a target area.
I looked up the parts list for the collision avoidance system on a 18 Corolla and it references a “mm wave radar sensor” near to the location I mentioned above. I next Googled what a mm wave radar sensor looks like on a Texas Instruments Corp website, but what I saw didn’t look like that. What I saw looked more like a laser diode.
fyi, Google the following to see what a mm radar sensor looks like.
Texas Instruments IWR1642 76-81GHz mmWave Sensors
Apparently, Toyota collision avoidance uses laser and pedestrian detection uses both radar and camera- https://www.toyota.com/safety-sense/details/feature/pcs
Pre-Collision System with Pedestrian Detection (TSS-P 25)
This is what @TwinTurbo 's link above says about the 2018 Corolla Collision Avoidance System
Using an in-vehicle camera and radar to help detect a vehicle or a pedestrian in front of you, the Pre-Collision System 26 with Pedestrian Detection 36 (PCS w/PD) can help you mitigate or avoid a potential collision. If the system determines that a frontal collision is likely, it prompts you to take action using audio and visual alerts. If you notice the potential collision and apply the brakes, PCS w/PD may apply additional force using Brake Assist (BA). 27 If you don’t brake in time, it may automatically apply the brakes to reduce your speed, helping to minimize the likelihood of a frontal collision or reduce its severity.
Maybe what I saw that looked like a laser diode is actually the camera, and the radar sensor is somewhere nearby.
I re read and it says uses laser OR radar in conjunction with camera:
Using an integrated camera and laser or radar to help detect other vehicles in front of you, the Pre-Collision System (PCS) 26
If you have only collision detection it can get by with just laser. To detect people as well, radar would be better suited is my guess.
I can find no precise description of how it works in a 2018 Corolla, but in a 2017 here is what it says:
The millimeter wave radar sensor assembly and forward recognition camera detect the position and relative speed of preceding vehicles and pedestrians
On a '17, it appears the forward looking camera is in the rear view mirror area, possibly part of the rear view mirror ass’y. The mm wave radar sensor looks to be in the front grill area, but higher up (near the hood latch), not where the gadget I thought was a laser diode. That must be some other kind of sensor.
Good luck to a diy’er if that system ever goes on the fritz …
Almost every system now uses both optical cameras as well as radar. The systems are working great based on real-world testing. They take very little getting used to and false positives have been reduced quite a bit in just a handful of years. Almost evry car now has a high-mounted camera above the rear-view mirror. I am posting an image of the camera in a Subaru. The radar is almost always just behind the grill and most automakers now use a logo as the cover for it.
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And where those anti-collision gadgets are located on the car?
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Right up behind the rear-view mirror, up against the windshield
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George, tell your friend to stop tailgating and the system will leave them alone! 
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Regarding the comment about these systems not being a Do it yourself repair, that is true about a lot of things on modern vehicles. If the collision warning fails and the person does not want to spend the money to fix it here is solution. Just look out the thing called a windshield and leave space between vehicles.
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Our 17 rav4 has that. The salesman was at a demo, it was raining and did not stop for the target. His advice, don’t depend on it.
Maybe, just maybe, those systems will finally teach chronic tailgaters that their preferred driving style is dangerous and wrong. I’m sure that I’m not the only forum member who has people tailgating me when I am already driving over the speed limit, and the presence of cars in front of me makes it impossible for me to go any faster.
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They’re not “tailgating” they’re “drafting”! lol
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I had a Cadillac do that the other day. Close enough I was tempted to invite them inside! 
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When I was still a teenager there was a common ‘tongue-in-cheek’ complaint among drivers that 9 out of 10 Cadillac and Chevrolet Suburban owners did not check ‘turn signals’ on the option list.
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amen to that
90% of the time that I’ve been stuck in stop and go 5 MPH traffic i find 5 or 6 moron tailgators slammed into each other to be the cause of the “accident”
Any competent driver hates tailgaters. Yet there are so many of them. I remember one a few days ago driving a few feet from my rear bumper on local city streets. I finally pulled over and let him by.
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My wife saw a bumper sticker the other day that read;
If you are close enough to read this
You’d better have some lube!
We own 04 and 15 Camry’s. Rented an 18 Camry last fall with "enhanced " cruse control and some sort of “collision avoidance” “feature”. Driving on a 4 lane freeway through rolling hills of Illinois the car constantly shifted down going up gentle grades and again going down: 8-7-6-7-8-7-6-7-8…About drove me crazy. The worst however was in minimal traffic while following a semi in the right lane. I’m watching a car approach in the left lane while I’m creeping up on the semi. I’m calculating the differential speeds of the 3 of us and planned to move out into the left lane behind the passer on my left and follow him past the truck. Not obstructing any of us.The damn computer decides I’m too close to the semi ( 10 car lengths maybe) and slows down my car. I eventually figured out how to turn off this “feature” and never used the cruse again. I’m old and I’ll probably never buy another new car, certainly not one with this sort of “safety feature” on it. Help strikes again.