Photos: Which of these smartwatches will you be wearing this year?

Google has joined the ranks of tech companies hoping to stimulate the smartwatch market. The company this week unveiled its operating system for wearable technology, Android Wear, and revealed that the first hardware running it will be available later this year.

This is LG's Android Wear-powered device, the LG G Watch, which is expected to launch sometime in the second quarter of this year.

Here's Motorola's Moto 360, which the company said will be available this summer. The watch is voice controlled, using Google Now — the wearer can say "OK Google" to ask questions, send a text or set an alarm.

Here's another view of the Moto 360. Other companies working on Android Wear-powered devices include Asus, HTC and Fossil, which has a long experience of building smartwatches.

But Android Wear-powered devices aren't the only ones to go on sale soon — all sorts of companies are trying out different models combining the features of a watch, a smartphone and the increasingly popular fitness band.

Samsung's Gear 2 and Gear 2 Neo smartwatches (seen above) will go on sale next month, allowing wearers to accept or ignore incoming calls and messages, and receive notifications. Both use the Tizen operating system.

The Gear 2 packs a two-megapixel camera, accelerometer, gyroscope, and heart rate monitor, plus a standalone music player with Bluetooth headset support, with 512MB of RAM and 4GB of internal memory in a 36.9 x 58.4x 10.0 mm, 68g product.

The camera-less Neo is oddly slightly larger but lighter. Google has said that it is working with Samsung on Android Wear devices, too.

They can also be used to control the devices such as TVs and set-top boxes using the WatchON Remote application and an embedded IrLED sensor.

The Samsung Gear Fit, also due to be available next month, features a 1.84-inch curved Super AMOLED display (at 432x128 resolution) and combines some of the capabilities of a fitness band with a smartwatch.

It functions as a pedometer and heart rate monitor, but also displays notifications from Galaxy smartphones, including incoming calls, emails, SMS, and alarms.

It's hardly the first time that tech companies have a had a go at developing smartwatches. They've been at it for more than a decade, but with little success — check out our gallery detailing the long history of smartwatches including these Microsoft Spot watches from 2006.

And the big question is what — if anything — Apple will do. Most of what is happening with smartwatches now is just about jockeying for position on the starting line; the race may only really begin if Apple decides to join in.