How to use opencv extra modules?

Why would one use electrical magnets to hold the modules for a modular smart phone?

• I read that project "Ara" funded by Google to develop a modular smart phone wants to use electrical magnets to hold the modules in place. I find this design choice rather hard to believe: Why should the magnets be electric? Maybe to be able to disengage a module by software? Why don't they use permanent magnets to hold the modules in place? An electrical magnet needs current to operate. I understand that the current needed, when the gap between the 2 surfaces is near zero, is rather small compared to the situation when you have to attract something from a distance. But this would drain the battery, depending on the weight of the modules you need a force to hold them in place if the phone gets shaken for example. Battery operation time is already a scarce resource for smart phones. What happens if the battery is empty, will the phone fall apart and the modules will fall out unless you charge it?

• Answer:

  Project Ara is using electro - permanent magnets. The magnets switch from a magnetic to non-magnetic  state, and back again, under control of an electric pulse. But they consume no power when in either state.