And in Baltimore, a group of high school students are tackling the drug overdose epidemic by building a cellphone app that alerts people when a toxic batch of heroin is being distributed in their area. The students, who are mostly African-American, helped design and build “Bad Batch Alert,” which sends text messages to alert Baltimore residents when people in their area are overdosing at a higher rate, likely from a tainted batch of the drug. The app also allows users to text for help, allowing drug users an alternative to calling 911 in the event of an overdose.