Homes were evacuated after a lighter shaped like a grenade was found outside a synagogue in Golders Green.
Police were called following the discovery at a synagogue in Bridge Lane at around 4.30pm on Monday.
The item was inspected by bomb squad officers and confirmed to be a novelty lighter, local neighbourhood watch group Shomrim said.
Builders were erecting a fence behind the synagogue when they made the discovery.
Shomrim tweeted: “A grenade has been found outside a synagogue in Golders Green. @MPSBarnet and @metpoliceuk bomb squad on scene.
“All neighbours have been evacuated as a precautionary measure. Hillcrest Avenue at the junction with Bridge Lane is closed in the interim.”
They later wrote: “Suspected grenade found outside a synagogue on Bridge Lane in Golders Green has been confirmed to be a novelty lighter.”
