The invisible wall: Portions of Trump's planned border wall between the US and Mexico might use electronic surveillance methods instead of physical borders

• Trump's planned border wall between US and Mexico might not be visible
• Homeland Security Secretary John Kelly said the wall could use 'technological sensors' in many areas
• Trump previously said he'd build 'big, beautiful wall' and make Mexico pay for it 
• Much of the 2,000-mile border already has mixture of physical and virtual walls

Donald Trump's planned border wall between the United States and Mexico might not be all that visible, Homeland Security Secretary John Kelly said.

Trump had previously said he'd build a 'big, beautiful wall' for which Mexico would then pay - but it appears the actual wall may leave more up to the imagination.

Instead, the wall could use electronic surveillance methods to create a sort of virtual wall.

Scroll down for video

Kelly told Fox News: 'Any discussion about the protection of our southwest border involves discussion of physical barriers but also of technological sensors.'

Fox News reporter Catherine Herridge elaborated: 'There will be the physical wall and then parts of the wall that you can actually see through because it will rely on sensors and other technology.' 

Kelly said the wall would be built 'where it's needed first' before expanding to something that may not end up resembling Trump's plan for a great wall along the nearly-2,000 mile land border between the US and Mexico.

He hopes to complete it in two years and claims funding will come 'relatively quickly.' 

It is not yet clear how the wall might be funded.

Much of the barrier between the United States and Mexico already has a mixture of walls along urban areas and other heavily-trafficked regions and 'virtual fences' along more remote stretches, the Independent reported.