Forget Black Friday. The notion that you need to ruin your Thanksgiving by standing in line all night to get the best deals on everything from electronics to toys is just so last year.

This year, a handful of young technology companies promise to get you refunds if you paid more than the Black Friday or Cyber Monday price when you shopped in person or online. They do that by taking advantage of little-known retailer and credit card “price guarantees” that few people monitor because it’s too much trouble.

The sites Paribus, Earny and Slice are offered for free, though Earny will take a portion of the savings if the company lands you a refund.

Each site is a little different, however. And they don’t necessarily play well together, so you may have to choose your favorite. Here’s how they work:

Paribus: Sign up, and Paibus will track all online purchases made with the 30 retailers that it follows. Most of these retailers, which include Nordstrom, J. Crew and Costco, have corporate policies that allow consumers to get partial refunds if the price on a purchased product drops within a set time frame, which vary from retailer to retailer. Bloomingdales, for instance, will adjust the price if it drops within 10 days of your order. Costco will adjust when a price drops within 30 days of purchase.

To initiate coverage, you simply sign up with Paribus and provide your email and Amazon credentials. Paribus will search your emailed purchase receipts and automatically apply for refunds any time a price drops by more than $3 during the retailer’s price-guarantee period. The price-checking service is done automatically by scanning your email receipts by item number.

Better yet, Paribus’ service is 100 percent free. The company used to charge a commission, but it dropped all charges when it was purchased by credit card giant Capital One a year ago.

Paribus tracks only online purchases, however. If you shop in person even if you had the receipt emailed it doesn’t help you. And if your retailer doesn’t provide a price guarantee, Paribus doesn’t attempt to get a refund from another source, such as your credit card company.

Notably, while Paribus tracks sales on Amazon, the online retailing giant offers no price guarantees. Paribus can get you a refund from Amazon only if your packages don’t show up on time. In that case, Paribus would apply to recover your shipping charges or, if you’re a member of Amazon Prime, a rebate or a free extension of your Prime membership.

Holiday shoppers should also know that three retailers Target, Best Buy and Walmart suspend their usual price guarantees from Thanksgiving to Cyber Monday. If this is where you plan to do most of your holiday shopping, Paribus will be of little use.

Earny: On the other hand, Earny tracks both in-person and online purchases, seeking refunds from both retailer and credit card policies. Thus, if you bought a product at Amazon, which offers no price guarantee, but could have gotten it cheaper within the 60-day window provided by your credit card’s price guarantee policy, Earny will claim the refund from the credit card company.

Because most big credit card companies, with the exception of American Express, provide at least a 30-day price guarantee on the items you bought with plastic, Earny maintains that you don’t have to worry about Black Friday at all.

The one catch: If you buy items in person, you need to have the retailer email the receipt for Earny to track it. And Earny will keep 25 percent of the savings as its fee.

Slice: Much the same way as Paribus, Slice finds purchase receipts in your email inbox and automatically compares those to current prices during the merchant’s price-guarantee period. Though it also notes that Amazon offers no price guarantees, Slice will provide refunds when you overpay for Amazon products anyway.

The site has a price-protection plan that will kick back the lesser of $10 or the actual price difference if the price of something purchased on Amazon drops within seven days. However, the most any given consumer could claim with this policy is $20 during the 2017 holiday season.

Notably, Slice doesn’t claim refunds for you. It will notify you when a refund is available and send you a prepopulated email that you simply need to send to the retailer, said spokeswoman Julia Handel. You need to take the step of forwarding that email on to the retailer to obtain your refund.

This app, which works with both iPhones and Android devices, will also notify you about product recalls and other product safety warnings.

Consumer finance expert Andrea Woroch said these apps are particularly helpful because no one has extra time during the holidays. Even if you knew the price-guarantee policies offered by your credit card companies and the retailers where you shop, trying to track the price changes of all the products you might buy during the holiday season is practically impossible.

“You are seeing fluctuating prices online to keep up with demand, but that means you could pay too much if you bought at the wrong time,” she said. “That’s what makes these apps so great. You don’t have to fight the crowds, or even wait to shop on Black Friday. These apps will do the price checking for you and just drop the savings into your inbox.”