The Best Robot Vacuum I’ve Ever Tested Is 40% Off Until Prime Day Ends Tonight

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Prime Day 2025 ends tonight, and Lifehacker is sharing the best sales based on product reviews, comparisons, and price-tracking tools before it's over. 

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• New to Prime Day? We have a primer on everything you need to know. Sales are accurate at the time of publication, but prices and inventory are always subject to change. 

Robovacs, generally, work best in homes with no clutter: no cords, big open spaces, not a lot of things on the floor. The sweet spot for robot vacuums is dust or some basic dirt. But that's not what most people have in their homes: They have pets. They have children. They have small houses packed with stuff. Most people get a robot vacuum in the vain hope it'll simply take care of the floor, with no help needed. Most robots are going to get caught up on all that clutter, and you'll spend all your time unclogging them or rescuing them from where they're stuck—and you'd need to still keep a broom and a mop around, and supplement the robot's work. The 3i S10 Ultra is different.

The 3i's main schtick is that it never needs you to change the water, because it can do that for you. It boils the water when the robot returns to the dock, and the resulting distilled water is sanitized and ready to go. If the robot runs low on water, it makes it own via an on-board dehumidifier. I haven't changed the water once.

But as convenient as is, it would mean nothing if the robot couldn't clean. The 3i S10 was the first robot I ever tested that got large pieces of mulch and pet toy floof off the floor and into the vacuum without rattling around or clogging the vacuum. Then the tower evacuated the vacuum when it docked. The 3i has two large sweeps at the front of the robot that rotate in opposite directions to move debris towards the rollers. A singular roller is shockingly effective at getting that debris off the floor and towards the vacuum, where 13000Pa sucks it all away. That's not even a lot of suction for today's premium robots, but here, it works. It's quiet, too. Blissfully so.

Then, the mop comes out. It's a roller, which I'm growing to enjoy more than any other kind, and it did a good job, even on the first pass. The navigation of the robot was also effective—the robot navigated the cords and maze of feet and dog toys under my couches without any issue. It didn't get stuck on the pile of laundry; it avoided it. It understood what was a dog toy to be avoided, and what was dog toy floof, to be vacuumed into oblivion.

There are a few notes: First, the tower weighs a ton—about 50 pounds. You won't want to move it once it's in place. Also, the robot itself is tall at over four inches, and the mop doesn't wash with hot water, just regular distilled water. Also, 3i is a new company, and that might give you pause. For me, none of these issues were noticeable or changed the outcome, which was a clean floor.

There are lesser vacuums for sale this week that are still more expensive than the 3i S10. For instance, I'd recommend this over the Saros 10, 10R or Dreame X50, all of which I liked and are considered premium robot vacuums. The 3i S10 is usually a tear-inducing $1,899.99, but right now it's down to $1,199.99 ($1,139.99 if you use the additional coupon code S10USAVE5 at checkout). Yes, it is still expensive, but at this sale price, it might be worth the splurge.

Looking for something else? Retailers like Walmart, Best Buy, and Home Depot have Prime Day competition sales that are especially useful if you don’t have Amazon Prime.

• Walmart’s Prime Day competition sale begins at midnight on July 8 and will include deals up to 50% off. It’s an especially good option if you have Walmart+. 

• Best Buy’s Prime Day competition sale, “Black Friday in July,” runs through Sunday, July 13 and has some of the best tech sales online. It’s an especially good option if you’re a My Best Buy “Plus” or “Total” member.