As the smartphone wars heat up, Apple has acquired a key technology in the arms race.

The company in recent months purchased Silicon Valley-based wireless chip developer, Passif Semiconductor, according to people briefed on the deal. Passif develops communication chips that use very little power. Its technology, which includes a radio that works with a low-energy version of Bluetooth called Bluetooth LE, is promising for health-monitoring and fitness devices that need extra-long battery life. (Apple, of course, is working on one of those.)

It isn’t clear how much Apple paid. The people said Apple tried to buy Passif a few years earlier for a price in the mid-tens-of-millions of dollars. Presumably it would be higher now.

An Apple spokeswoman said “Apple buys small technology companies from time to time.”

It’s easy to see why Apple wanted Passif, which was founded several years ago by Ben Cook and Axel Berny, who were PhD students at the University of California, Berkeley. As technology companies pack more battery-draining features into smartphones, technologies that preserve and extend battery life are critical. Radios are some of the biggest battery drainers.

The need is particularly acute for wearable devices, like activity-tracking watches. One of the reasons Apple and its rivals haven’t launched such devices yet is how hard it is to shrink screens, batteries and radios to fit into them.

Venture capital firm Khosla Ventures invested in Passif and still lists it on its website. How much the firm invested isn’t clear, although some trade publications announced it had invested $1.6 million in 2008.

There is no doubt that Apple has been picking up the pace of small tech acquisitions. (CEO Tim Cook said so in May.) Apple recently purchased indoor Wi-Fi company Wifislam and mapping data providers Locationary and Hopstop.

Some deals have been designed to land key talent in areas where the company is weak, like mapping and data science.

But the Passif deal is right in Apple’s wheelhouse: components for next generation devices. Apple has been ruthless about getting access to new technologies on favorable terms. The company years ago purchased two semiconductor companies to diversify from Samsung Electronics, its rival that supplies a lot of its components. In that effort, Passif too could help.