San Francisco-based Trulia, a national leader in the residential real estate search business, currently serves some 20 million unique monthly users.

And while it’s well established in the home sales market, more recently it has been moving aggressively into the rental space as well.

As anyone in the Bay Area knows, rental units can be hard to find these days. Trulia’s own figures show that rentals have gone up in price 11.1 percent in San Francisco over the past year (and 9.4 percent in San Jose.)

These changes in the rental market parallel the emergence of smartphones; thus the company's recent launch of a free iOS app, Trulia Rentals, provides some intriguing insights into how our lives are evolving in the mobile age.

The iPhone app joins Trulia’s Android rental app, which launched last September, in the reverse order of introduction chosen by most consumer-facing companies.

The Android app is great,” says Trulia’s Cristin Zweig. “The iOS app is amazing. It was designed to meet the specific needs of renters as opposed to buyers. Renters don't need to know the type of shingles on a roof for example. They need to know the cost, the amount of space, and when it became available. That’s a much smaller set of needs. Their number one need probably is timeliness. What's on the market right now?”

The urgency behind that question is of course due to the fierce competition for any affordable new units that come on the local market.

“The life cycle of a new rental unit is a day,” notes Zweig. “In fact it’s probably less, maybe only two-three hours.”

In order to meet this demand, the Trulia iPhone app has a built-in “push” capability.

It works like this: You set the parameters of your search (neighborhood, size of apartment, price) and Trulia will send notifications right to your phone whenever a new unit becomes available.

For the serious apartment-seeker, this certainly represents a competitive advantage over those using alternative methods (Craigslist, driving around neighborhoods, etc.)

In a recent survey of renters in San Francisco, the company came up with some revealing findings:

• 89 percent of renters own a smartphone.
• 69 percent of renters prefer to contact agents or landlords by email (as opposed to phone calls.)
• 91 percent say high-quality photos are the most important feature of an online rental listing.

Besides apartment-seekers, the migration to mobile by on-the-go home-buyers is becoming apparent as well.

“More than 30 percent of our weekend traffic is now mobile,” says Zweig. “They will literally pull up in front of a house and use our app to find out the asking price before even deciding whether to go in."

Trulia was started six and a half years ago by Pete Flint and Sami Inkinen, while they were still at Stanford Business School.  The company, which is headquartered in Soma, currently employs over 350 people in San Francisco, Denver and New York.