Electric measuring tools saves you the hassle of having to guess about measurements. There's no cord to restrict you, just make sure you've charged the battery.
From Amazon
testo 750-1 - Voltage tester
Hamilton Gas Products
Testo 750-1 Voltage Tester
AC One
testo 750-1 - Voltage Tester 0590 7501
Conrad Electronic
testo 750-1 Two-pole voltage tester CAT IV 600 V, CAT III 1000 V LED, LCD