Big-box retailers are developing indoor navigation tools to help shoppers find what they want. Some, including Target and Walgreens, have stored floor layout plans in smartphone apps. Walmart and Home Depot apps now can display aisle numbers for searched items. In May Walmart launched an "In-Store" mode in its app, and within two weeks about 15% of page views were from shoppers. But with mobile apps becoming a key sales channel, they've begun adding coupons, prices, store hours and bar code scanners. About 20% of retail sales are lost because shoppers can't find items, estimates Nathan Pettyjohn, CEO of Aisle411, an app with 9,000 store maps. Parenthetically, it's not just stores. One grad student at New York University's Polytechnic is developing an ambitious app, Wayfarer, to help new students find their way around campus and inside campus buildings.