Revealed: The tiny 20-byte patch that solved Apple’s most infamous iPhone scandal

If you’ve been an Apple user for a long time, you probably remember Antennagate – the drama surrounding cellular reception on the iPhone 4. As many users complained about the signal dropping considerably depending on how they held the phone, Apple released the iOS 4.0.1 update to address part of this issue.

Years later, designer and engineer Sam Henri Gold reverse-engineered the iOS 4.0.1 code to find out exactly what Apple did to change users’ perception of the iPhone 4’s antennagate problem. Spoiler alert: the entire patch required only a 20-byte update.

Remembering Antennagate

For those unfamiliar with the situation, the iPhone 4 came with a drastic redesign compared to the 3s. Instead of a plastic unibody back, the iPhone 4 was made almost entirely of glass with a steel frame that also functioned as wireless antennas for Wi-Fi and cellular.

Shortly after the phone hit stores, many consumers noticed that the cellular signal dropped if the iPhone was held firmly. It didn’t take long before the term Antennagate caught on and spread like wildfire on social media. At one point, Steve Jobs was so fed up with the discourse, he responded to a query from Ars Technica with a curt instruction: “Just avoid holding it in that way.”

A few weeks after the launch of the iPhone 4, Apple published a letter to the press discussing the issue in more detail. At the time, the company blamed the formula used to calculate how many signal bars iOS shows to represent the strength of the signal the phone was receiving.

“Users observing a drop of several bars when they grip their iPhone in a certain way are most likely in an area with very weak signal strength, but they don’t know it because we are erroneously displaying 4 or 5 bars. Their big drop in bars is because their high bars were never real in the first place,” Apple wrote.

The company also said in the letter that it would adopt a new formula recommended by AT&T to calculate signal strength more accurately. The new formula was released as part of iOS 4.0.1.

How iOS 4.0.1 recalibrated signal strength

Despite the letter and update, Apple never detailed exactly what changed in this formula. But now, thanks to Gold, we know exactly what Apple did at the time – and surprisingly, the development team only had to change a few lines of code.

As Gold shows in a post on X, the original formula used to calculate and represent signal strength in bars resulted in four or five bars of signal for most situations. This led users to believe they had great signal reception when they didn’t.

When the signal was really weak, the number of bars shown on iOS would suddenly drop to two or just one. This naturally occurred when users were holding the phone in their hands, which led people to believe that there was some kind of malfunction with the phone.

With the updated formula, the drop from each bar was much smoother and more accurate, so that users would no longer think they had excellent signal reception when they actually didn’t. And as such, the drop-off in signal when held a certain way wasn’t nearly as drastic.

You can see a comparison of the two formulas in the chart above, with red representing the bars in iOS 4.0 and blue in iOS 4.0.1 with the new formula. The closer to zero dBm, the better the signal.

With iOS 4.0.1, Apple also changed the height of the signal bars shown in the iOS status bar, a small touch that probably helped reduce alarmism about weaker signal reception on the iPhone.

Apple’s path to a hardware fix

Even so, Steve Jobs wanted to ensure that most iPhone 4 consumers were happy with the product, not just the fix. A few days after publishing the letter, Apple held a small press conference in which it shared more details about how the company conducted laboratory tests on the iPhone 4 antenna.

To help reduce tension, Apple provided all iPhone 4 buyers with a free bumper, which prevented users from directly holding the phone near the antennas and blocking the cellular signal. Apple recently brought back its bumper case for the iPhone Air, but this time it’s for protection and aesthetics.

A year later with the launch of the iPhone 4s a year later, Apple repositioned the antennas on the stainless steel frame, putting an end to the antennagate problem, which suggested the design was actual a problem. But for millions of iPhone 4 users, a small bit of code made all the difference.