Santander is a picturesque coastal city - the sound of waves, crashing on the seawall, provides a gentle backdrop to daily life. Aside from the occasional ferry from England, the town in the northeast of Spain doesn't get too many foreign visitors.

It turned quite a few heads, then, when delegations from Google, Microsoft and the Japanese government all landed here recently, to literally walk the city streets.

What they've been coming to see though is mostly invisible: 12,000 sensors buried under the asphalt, affixed to street lamps and atop city buses. They silently survey parking availability, and whether surf's up at local beaches. They can even tell garbage collectors which dumpsters are full, and automatically dim street lights when no one's around.

"You see the two antennas? You see, just behind the trees?" he said, pointing at a box which looks a little like a wireless router. "Those antennas are gathering the information coming from the sensors under the ground, and they send it to the command and control center. It's well-integrated, it's seamless."

Santander is one of four cities in the UK, Germany and Serbia where sensors are being tested. But with about 180,000 residents, Santander is small enough to achieve full saturation with these devices. So it's become Europe's prime testing ground for expanding this technology elsewhere on the continent.

Munoz pointed out sensors and digital panels around downtown Santander that display the number of available parking spots on every street.

"Once a car parks on top of the magnetic sensors, the magnetic field changes. This is detected by the sensor, and then we update the information in the database, and this is depicted on the panels," he explained from his car seat.

The sensors send data to a command and control center - and also to a suite of applications on citizens' smartphones. This includes real-time information on road closures, parking availability, bus delays and even the pollen count. Citizens can contribute too, by taking a smartphone photo of a pothole or broken streetlight, for example, and uploading it directly to city hall. There's an app for that as well, Munoz explained.

Mayor Inigo de la Serna rattles off the list of big corporations with which his once-sleepy city is now doing business.

"We have signed agreements with NEC from Japan. With Ferrovial, a service company. With Telefonica, of course. With IBM for the Santander City Brain. [And] with the Bank of Santander for a new kind of payment device," he said.

Perhaps as you might expect for a smart city, the mayor pulls out his iPad and demonstrates the Santander City Brain - an app where he floats ideas and citizens can weigh in.

"People have already sent us about 400 different ideas. Very, very interesting. So [it's as though] the citizen is sitting with us, telling us 'I want to work to make this city better. I don't want to just complain.' You know?"

Complaining is something that many public officials in Spain hear a lot of these days. Spanish streets often erupt in angry protests over the economy. But Santander has managed to buck the trend. People are using their smartphones to make their city better. The city saves money - about 25 percent on electricity bills, and 20 percent on garbage - and utility companies pick up the tab for the sensors' upkeep, precisely because they too save money by using them.