Microsoft, the multi-national technology group, has hired a fleet of robotic security guards to patrol its Silicon Valley headquarters.

The 5ft-tall, 300lb K5 robots have been developed by Knightscope — a start-up company based in Mountain View. Seven have been built so far, and the company plans to deploy four of them before the end of the year.

The robots are designed to detect anomalous behaviour — such as someone walking through a building at night — and report it to a remote security centre. Their dome-shaped bodies contain cameras, sensors, navigation equipment and electric motors, which are all powered by a large rechargeable battery.

Each robot has four high-definition cameras plus a licence-plate recognition camera, four microphones and sensors to measure the barometric pressure, the temperature and carbon-dioxide levels.

A combination of GPS and laser ranging helps the robots to find their way around their patrol area and avoid obstacles.

They can work for about 24hr on a single charge, but they are programmed to go to a charging pad when necessary. It takes them 15-20min to re-fuel. Knightscope is charging Microsoft $6.25 an hour for each robot. This is half the average wage of a human security guard.

Stacy Stephens, Knightscope’s co-founder and vice-president of sales and marketing, said: “The K5 will take care of the monotonous and sometimes dangerous work, leaving the strategic work to law enforcement personnel or private security.”