Malaysia Airlines flight 370 carrying 239 people left Kuala Lumpur and vanished. Six days later theories abound -- but hard data on what happened to the plane and its cargo remains scarce.

Authorities have an abundance of resources: data sources aboard the plane itself, radar scopes on nearby ships, military and commercial imaging satellites, and more. On Friday India began searching hundreds of uninhabited islands in the Andaman Sea using heat-seeking devices, officials said, declining to give further details about the technology.

Here’s a look at the other tech officials are using in the hunt.

Radar imaging

The main tracking tool for flights -- missing or otherwise -- is radar, which uses relay stations on the ground to emit radio waves that bounce off objects. The returning signal provides the location of the object, but tracking by radar becomes increasing difficult over open water. And without a wealth of base stations on the open sea, there are vast holes in radar coverage large swaths of water.

This lack of coverage has made the search for flight MH370 difficult. The search now includes areas of the vast Indian Ocean after military radar on a small island in the Strait of Malacca was able to track the flight before it went missing.

On Friday Malaysian officials said they had established with a "more than 50 percent" degree of certainty that military radar had picked up the missing plane, spotting a blip moving west across the Malay Peninsula into the Strait of Malacca

Sonar imaging

When and if MH370 is found, it will likely be done so through Sonar. This underwater version of radar sends sound waves into water and uses the reflections to locate an object. Sonar was used to find the main section of Air France flight 447 after it crashed into the Atlantic off the coast of Brazil, 2.5 miles underwater.

Sonar also determines the density an object, whether it is a hard or soft reflector. A hard reading is usually indicative of metal from a ship or aircraft.

Sonar will likely be used to located MH370’s “pingers” which will send a signal from the black box. The “ping” automatically goes off once a plane has crashed into water. The country of Malaysia has two submarines with sonar but has not yet used them in the search. There were reports that fishermen were joining the search and using their sonar to help locate the plane.

Satellite imaging

Satellite imaging company DigitalGlobe told FoxNews.com it had redirected five satellites to the area to help scan the waters for signs of the missing planes. The company is also using its crowdsourcing platform Tomnod to let the public comb through its image banks.

“There are several viable scenarios that authorities are pursuing and DigitalGlobe is laser focused on tasking its satellites to monitor any/all relevant areas,” spokeswoman Risa Kleen said.

The company said it has added about 15,000 square miles of imagery to the Tomnod site. It says that 3 million registered users have looked at every pixel at least 30 times. An additional 8,700 square miles are being added over the next 24 hours, including a new area in the Indian Ocean.

Radio

Tried and true radio can also be used to locate a plane, as as most systems will send a distress signal before they go down. In addition, most black boxes transmit a radio signal as well when a plane crashes. If the crash occurs over water, the signal does not travel over a long range.

Pilots themselves are a key way for airplanes to stay in touch with air traffic controllers. The last-reported radio transmission from the cockpit of flight 370 was "Alright, good night," just before the craft crossed into Vietnamese airspace.

GPS satellites

Several online flight-tracking services can locate airplanes in real-time, using GPS navigation data transmitted from the aircraft themselves. But in the case of Malaysia Airlines flight 370, which disappeared from radar screens more than 48 hours ago, a hole in coverage maps means even these sites lack answers.

“We lost tracking for it pretty early on,” a spokesman for FlightAware, one such site, told FoxNews.com earlier this week.

FlightAware published a minute-by-minute tracking log of the flight. The plane was at 35,000 feet at 1:01 a.m. Saturday morning. One minute later, the site’s data ends.

“Government regulations prohibit live flight-tracking in the area,” the company explained. “Quickly after take-off, it was outside our coverage range and we had no live position.”

FlightRadar24, another real-time flight tracking app, immediately sought to analyze its data following the plane’s disappearance. The site appears to have slightly more data, tracking flight 370 for another 15 or so minutes. Yet it, too, could not track the plane completely.

Flyht Aerospace Solutions makes a next-generation black box system called AFIRS (Automated Flight Information Reporting System), which transmits a plane’s position every 5 to 10 minutes via the Iridium satellite network, and every second when it detects an abnormality. Had it been on board, it might have helped pinpoint the plane’s whereabouts.

Visual data

To find a missing plane, authorities carve up the search area into giant swaths of land and sea. Airplanes and boats then scour individual cells of the grid looking for evidence of wreckage, or anything that might point to the plane’s whereabouts.

Because the area is so enormous -- 35,000 miles or so -- the search is painstaking and slow. Aircraft at low altitudes can only cover 18 or 19 square miles in 8 hours, Digital Globe said.

Signals from onboard

Airplanes give off several types of signals via transponders, text messages, and in some cases, satellites. Transponders are electronic devices that automatically identify commercial aircraft within air traffic control radar range and transmit information on the plane's identity, location and altitude to ground radar stations.

ABC News quoted two unidentified American officials as saying the U.S. believes the plane's data reporting system and transponder went dark separately, at 1:07 a.m. and 1:21 a.m.

There is a maintenance data stream known as ACARS (the Aircraft Communication and Recording System), a decades-old system -- arguably an outdated one -- that is essentially a digital link for text messages, but can’t transmit flight data on demand or continuously. ACARS sends pulses of information about the condition of the aircraft for maintenance purposes.

A source familiar with the investigation but not authorized to speak on the record told Fox News chief Intelligence correspondent Catherine Herridge that flight 370 continued to send “periodic pushes” of data after the transponder went dark, suggesting the jet did continue to fly. This was described to Fox News as signals data different from the ACARS data that, in isolation, would not provide location data.

While the source said they could not discuss specifics about the “periodic pushes of data,” they said it went beyond the standard maintenance information.

Boeing provides a service called the Health Management System, which provides real-time data via satellite. But a source told Fox News Malaysian airlines was not a client of the Boeing service.

Cellular signals

Locating the hundreds of mobile phones that vanished along with the plane isn't as simple as activating a "Find My iPhone" app, especially considering the speed the plane was traveling, its altitude and the fact it was probably flying over water.

In addition, airplanes still require people to put phones in “airplane mode” that disables many of the radios on them, notably the cellular connections. And even if some left their phones active, they wouldn’t connect with a tower given the speeds planes travel at -- and the fact that there just aren't cell towers over the open ocean.