Months before its rumoured September release date, wild speculations continue to swirl on fresh iPhone 5S offerings, which analysts love to call as killer features to neutralise the iOS smartphone's numerous rivals.

The latest of them leaked out via a new handset concept and a freshly-unveiled iPhone accessory, the details of which are discussed below.

A slightly redesigned iPhone 5S with Retina+

Earlier this week, reports came out that the 5S is getting twice the Retina dose deployed with the iPhone 5. While the screen size remains at 4-inch, the pixel is boosted by as much as 1.5 million, effectively doubling what was seen last year.

Along with generous upgrade comes a bit of rework on the front face of the handset - users should notice an expansive phone screen with virtually no-bezel surrounding all sides of the more immersive viewing window.

A possible bonus is the various colour options besides the standard black and white casing, which remains a fusion of aluminium at the back and Corning Gorilla Glass 3 at the front section.

The 5S shooter is with dual capabilities

While the iPhone 5S main cam is still a toss between a 12MP and 13MP sensor, almost certain additions are dual-LED flash and dual-shot style, the latter to be packed with the re-engineered iOS 7 that Apple will let out early next month.

Hardly an original, the latter is closely similar to the camera feature that Samsung has introduced via the Galaxy S4.

Robust handset security in iPhone 5S

Almost every 5S rumour and render is with the fingerprint sensor that reports said will be embedded beneath the handset's Home button, amply protected by a sapphire coating. The new iPhone 5S picked up by Gotta Be Mobile is no different, showing off a device security protocol that would limit access to iPhone owners only.

While there were reports that production issues could bump off the feature, some analyst are convinced that the refreshed smartphone will deliver stronger security come its unveiling moment.

The iPhone 5S is a wireless key

The last exciting feature is made possible by a companion product called August smart lock from Yves Behar. The mechanism, according to Apple Insider, installs on a door lock and using Bluetooth connection, pairs with the iPhone 5S or older models.

The device is pretty much plug-and-play. Once it is set, iPhone 5S users can use their handsets as their way of entry to August-capable door locks. The whole package runs on two AA batteries and should last six months without replacement. It has a failsafe physical controller or a dumb alternative just in case something goes haywire with the smart functions.

This accessory, however, is not cheap. Pre-orders will commence on August for $US199 or about the same price of new iPhones with contract.