QMTL via Amazon offers the Tacklife Outlet Power Tester for $9.97. Clip the 40% off coupon (click the "Redeem" button under "Applicable Promotions") to cut that to $5.98. Plus, Prime members bag free shipping. That's $17 off, tied with our March mention, and the lowest price we could find. It features three indicator lights and a nominal voltage range of 50 to 60Hz.