A utility meter clamping ring is locked to the meter by a locking device that locks the free ends of the ring together automatically without the use of a separate plunger device. A latch is spring loaded in the locking device housing in a normally biased lock position. The lock device is secured to one free end of the clamping ring. An apertured blade is attached to the other free end of the clamping ring. The ring is placed about the flanges of the meter cover and base flanges and the blade is then inserted into the locking device housing where its aperture is engaged automatically by the spring loaded latch and locked to the housing upon insertion. A conventional plunger key may optionally be used to unlock the latch and release the blade from the locked position to free the ends for removal of the meter cover via an optional bore in the latch engaged by the key. The latch may be optionally permanently locked to the blade so that either the locking device or the ring has to be destroyed. Weakening grooves are in the ring of the latter embodiment to facilitate breaking the ring open. Embodiments are disclosed for use with F and G type plunger unlock keys and include an anti-tampering sleeve for use in the lock to preclude tampering disengagement of the lock of the type used with an F type key.