The 5s features upgrades mostly in the form of internal hardware; it introduced the Apple A7 64-bit dual-core system-on-chip, the first 64-bit processor to be used on a smartphone, accompanied by the M7 "motion co-processor".

Reception towards the device was positive, with some outlets considering it to be the best smartphone available on the market due to its upgraded hardware, Touch ID, and other changes introduced by iOS 7.

[17] Before its official unveiling, media speculation primarily centered on reports that the next iPhone would include a fingerprint scanner; including Apple's 2013 acquisition of AuthenTec, a developer of mobile security products,[18] references to a fingerprint sensor on the home button in the beta release of iOS 7[19] and leaked packaging for an iPhone 5s showing that the traditional home button now had a metallic "ring" around it.

Similar ring-based imagery was seen on the official invitation to Apple's iPhone press event in September 2013, where the new device was unveiled.

While the iPhone 5s was expected to continue on sale until September 2016, replacing it and its A7 processor early meant that Apple "just reduced its long-term chip support window by a year" for iOS.

[50][51][52] The home button on the iPhone 5s incorporates a fingerprint recognition system known as Touch ID, based on technology from AuthenTec, a company that Apple had acquired in 2012.

Fingerprint data is stored in an encrypted format within a "secure enclave" of the A7 chip itself, and is not accessible to any other apps or servers (including iCloud).

[60][61] An analysis by GSM Arena suggests that the image quality of the supposedly 720p slow-motion footage resembles approximately 480p.

[63] According to technology commentators, the design of the earphones is aimed to improve sound quality by allowing air to travel in and out more freely.

[64][65] Apple states that the design of their earphones allows it to "rival high-end headphones that cost hundreds of dollars more".

[74] During the keynote, Apple announced a case for the iPhone 5s that was made of soft microfiber on the inside and leather on the outside.

Walt Mossberg of All Things Digital gave the phone a favorable review, saying that Touch ID "sounds like a gimmick, but it's a real advance, the biggest step ever in biometric authentication for everyday devices," and labeled it "the best smartphone on the market.

"[12] David Pogue of The New York Times praised Touch ID, but said that the innovation of the smartphone market has been saturated, and "maybe the age of annual mega-leaps is over."

He focused much of his review on iOS 7, which he believed was the biggest change of the device over previous generations, praising new Siri features, Control Center, and AirDrop.

[80] Darrell Etherington of TechCrunch who praised the iPhone 5s as the best smartphone available said "looks may not be different from the iPhone 5, but the internal components have a dramatic impact on day-to-day activities normal for a smartphone user," and went into detail explaining the impact of the improved camera and specifications on the phone.

[81] Myriam Joire of Engadget found that the iPhone 5s could benefit significantly from the A7 if developers created applications optimized for the 64-bit processor.

[82] Anand Lal Shimpi of AnandTech praised the phone's A7 processor, describing it as "seriously impressive", and stated that it was the most "futureproof of any iPhone ever launched.

As much as it pains me to use the word futureproof if you are one of those people who likes to hold onto their device for a while – the iPhone 5s is as good a starting point as any.

"[83] Scott Lowe of IGN also spoke highly of its 64-bit processor, "which has a substantial lead in processing power over the HTC One and Samsung Galaxy S4, accounting for a graphics boost of up to 32% and 38% in CPU benchmarks."

The debut of Apple's 64-bit A7 processor took rival Android smartphone makers by surprise, particularly Qualcomm whose own 64-bit system-on-chip was not released until 2015.

Furthermore, the 5c's polycarbonate exterior received a mixed reception and was seen as a cost-cutting downgrade compared to the iPhone 5's aluminum/glass case; the 5s retained the latter design and looked even more premium due to its additional gold finish.

Plus, unlike the ubiquitous rounded corners of the 6, iPhone 5 didn't really look like anything else on the market at the time".

[90] On launch day, major in-stock shortages were reported in most stores, across all countries where the iPhone 5s initially went on sale.

[93] Some commentators questioned how Apple handled the initial release, as online pre-orders were not offered for the iPhone 5s, meaning large numbers of people queuing outside physical stores, with most in line not receiving a unit.

[101] A number of technology writers, including Adrian Kingsley-Hughes of ZDNet[102] and Kevin Roose of New York believed that the fingerprint scanning functionality of the iPhone 5s could help spur the adoption of the technology as an alternative to passwords by mainstream users (especially in "bring your own device" scenarios), as fingerprint-based authentication systems have only enjoyed wider usage in enterprise environments.

[104] Brent Kennedy, a researcher of the United States Computer Emergency Readiness Team, recommended that users not immediately rely on the technology, citing the uncertainty over whether the system could properly reject a spoofed fingerprint.

[105] Following the release of the iPhone 5s, the German Chaos Computer Club announced, on September 21, 2013, that they had bypassed Apple's new Touch ID fingerprint sensor by using "easy everyday means".

The group explained that the security system had been defeated by photographing a fingerprint from a glass surface and using that captured image to make a latex model thumb which was then pressed against the sensor to gain access.

The spokesman for the group stated, "We hope that this finally puts to rest the illusions people have about fingerprint biometrics.