Washington, Apr 5 (IANS): Beware of seemingly harmless free applications (apps) -- they could be draining your smartphone of 75 percent of its energy, just tracking your location and transmitting the information to advertisers and downloading ads, a study reveals.

"It turns out the free apps aren't really free because they contain the hidden cost of reduced battery life," said Y. Charlie Hu, Purdue University professor of electrical and computer engineering.

Because smartphone batteries must be small and lightweight, power consumption is a major issue, the researcher said.

Hu led the work to create a new tool called Eprof -- for energy profiler -- to analyze how much energy a smartphone app consumes, said a university statement.

New findings show that 65 percent to 75 percent of the energy used to run free apps is spent for ad-related functions.

"We performed an in-depth case study, the first of its kind, of six popular smartphone apps, including Angry Birds, Facebook and Android Browser," said Purdue doctoral student Abhinav Pathak.

The free Angry Birds app was shown to consume about 75 percent of its power running "advertisement modules" in the software code and only about 25 percent for actually playing the game. The modules perform marketing functions such as sharing user information and downloading ads.

"We believe it is mainly to provide information about the user's geographical location so the ads can be more targeted or customized to that location," Hu said.

An application may contain tens of thousands of lines of code, broken down into many components called subroutines, threads and processes.

Eprof maps how much energy comes from each component, representing a new way for researchers to study smartphone energy consumption without using a power meter, an expensive and cumbersome piece of lab equipment.

"Eprof tells you how much energy is spent where," Hu added.

These findings will be presented at the EuroSys 2012 conference April 10-13 in Bern, Switzerland.