Seven states now permit the sale of e-cigarettes in jails, and, as one recent report noted, e-cigs “have quickly become one of the most sought-after items in jail commissaries.” Perhaps that’s not too surprising: Real cigarettes are banned in federal prisons, but e-cigarettes are largely unregulated.

But the seedier underbelly of the jail e-cig boom is that it’s not being driven by inmate demand. In fact, it’s actually the sheriffs who want them the most. Why? In a nutshell, money: E-cigarettes are a cash cow for county jails that receive commissions for every e-cig sold in the jail’s commissary.