Samsung and LG have announced more smartwatches ahead of next week's IFA trade show in Berlin, with an emphasis on connectivity and curvy faces.

Samsung Electronics announced the Gear S (below), its first smartwatch with 3G connectivity. Users can make or receive calls using the timepiece or get them forwarded from a smartphone, according to Samsung. That makes the Gear S one of the few smartwatches on the market that can act as a stand-alone device.

"The Samsung Gear S offers a new wearable experience with 3G connectivity and elegant curved display, expanding the smartphone experience to the wrist," a Samsung spokesman wrote in an email.

Powered by the Tizen operating system, it has a 2-inch, curved Super AMOLED display with a 360 by 480 resolution.

The Gear S has 512 MB of RAM, 4 GB of internal memory and a 300 mAh lithium-ion battery that lasts two days with typical use, the company said. Its sensors include a heart-rate monitor and UV monitors. It has also Wi-Fi and Bluetooth connectivity.

The watch will be available in phases starting from October, Samsung said, with pricing announced then.

LG G Watch R

The LG G Watch R (top), meanwhile, has a circular face, much like a traditional wristwatch and in contrast to most smartwatches released to date.

It seems designed to take on another round smartwatch, the Android Wear Moto 360 from Motorola.

"The G Watch R is lighter and more durable than other competing devices due to its unique Plastic OLED display," an LG Electronics spokesman wrote in an email. "It also has the best looking watch face (its a complete circle, unlike another recently announced round smartwatch which has a black bar running across the bottom) and the largest battery among available Android Wear devices."

Set in a stainless steel frame, the 1.3-inch display has a 320 by 320 resolution that can boost display clarity when viewed at different angles and under bright sunlight.

The company's earlier G Watch was criticised for its bland design and large, bulky display of 1.5 inches by 1.8 inches, and it had an LCD screen with 280 by 280 resolution.

The G Watch R, which has health and fitness tracking functions and an embedded heartbeat sensor, resembles its predecessor in terms of specs. It runs on Android Wear and is powered by a 1.2 GHz Qualcomm Snapdragon 400 processor, with 4 GB of storage, 512 MB of memory and a 410 mAh battery.

The dust- and water-resistant unit connects to Android smartphones via Bluetooth.

LG said it will roll out the device in the fourth quarter of 2014, but it did not give a specific date, region or price.

Both the Gear S and the G Watch R will be on display at IFA, which runs Sep 5 to 10.

Developing and designing apps for round displays

One of the issues developers have faced when creating apps for Google's OS is the fragmentation caused by different software versions, screen sizes and resolutions. The same problem has started to appear on smartwatches, albeit for now on a much smaller scale, as vendors launch square and round models of these devices.

Developers will have to get used to fragmentation in the smartwatch sector just as they have had to in the smartphone market, even if it will be painful, according to Neil Mawston, executive director at Strategy Analytics.

"There is no avoiding it with licensable OSes, because it's the only way hardware makers can differentiate themselves," Neil said.

The issue caused by round and square smartwatches hasn't gone unnoticed at Google. The company's Roman Nurik and Timothy Jordan, design and developer advocates on the Android Wear team, highlighted the issue in a blog post earlier this year.

To make notifications fit on the G Watch's square screen and the Moto 360, Roman and Timothy had to make some changes to the user interface of a walking tour app they developed. For example, they increased margins and moved some text and notifications on the round display.

Tools for smartwatch app design

The pair used the Android Design Preview tool, which lets developers mirror part of a computer screen to a connected Android device, to quickly see the effect of changes.

In general, designing for Android Wear is quite different from creating desktop, phone or tablet apps.

"You really need to think carefully about the information and actions you present to the user, and even more so about the contexts in which your app will come to the surface," Roman and Timothy wrote.

The key for Google and its hardware partners is to offer better tools than competing platform vendors and hot-selling devices, in order to appease developers.

"If you provide a better framework for smartwatch developers than your rivals, they are more likely to create apps for you. That creates its own positive spiral. But the main thing for developers will the installed base," Neil said.