Small drones or Unmanned Aerial Vehicles (UAVs) have been used by the military for several years, and now law enforcement agencies are looking to follow suit.

Miami-Dade Police Department (MDPD) are seeking permission from the Federal Aviation Administration (FAA) to deploy a 6.3 kg drone in the skies over their jurisdiction.

The drone is capable of hovering and training a surveillance camera that works at night as well as the day, thanks to an infra-red sensor.

"Our intentions are to use it only in tactical situations as an extra set of eyes," said Juan Villalba, spokesperson for MDPD.

"We intend to use this to benefit us in carrying out our mission."

SWAT teams could carry the tiny helicopter with them in a backpack, deploying it to provide vital intelligence in siege situations where the principles are barricaded.

Other law enforcement agencies are also in the process of evaluating the drones available on the market.

"The FBI is experimenting with a variety of unmanned aerial vehicles," said Marcus Thomas, assistant director of the Operational Technology Division at the bureau.

"At this point they have been used mainly for search and rescue missions."

"It certainly is an up and coming technology and the FBI is researching additional uses for UAVs."

Although law enforcement agencies are keen to use drones, the FAA have been reluctant to approve their use, due to safety concerns.

"You don't want one of these coming down on grandma's windshield when she's on her way to the grocery store," said Doug Davis, program manager for unmanned aerial systems at the FAA.

As a result, the FAA has attracted the ire of frustrated entrepreneurs wanting to sell their drones.

"We've had interest from dozens of law enforcement agencies," said Billy Robinson, chief executive of Cyber Defense Systems Inc, a start-up offering a 3.6kg drone.

"They are preventing a bunch of small companies such as ours from becoming profitable," he said.

Apart from safety worries, there are concerns from civil liberties groups about the prospect of surveillance cameras in the sky.

"There's been controversies all around about putting up surveillance cameras in public areas," said Howard Simon, Florida director of the American Civil Liberties Union.

"Technological developments can be used by law enforcement in a way that enhances public safety."

"But every enhanced technology also contains a threat of further erosion of privacy."