Nest has recalled its high-tech smoke alarm thanks to a design flaw that could stop it sounding quickly enough to be an effective alert during a fire.

The problem is with a wave feature, which allows customers to temporarily disable an alarm (or cancel a test) by vigorously waving their arms underneath the sensor. Unlike some alarms, you can wave up to eight feet below the Nest alarm, meaning you don’t have to look for a chair.

Unfortunately it turns out that Nest’s wave feature is too sensitive and/or can’t tell the difference between a waving arm and other movement. Although there are no reports of it happening out in the real world, Nest’s lab testing suggested it was possible the feature could thus mistakenly delay the alarm going off during a fire.

There’s been some confusion about the status of the “recall.” Nest announced the problems last month and halted sales, but didn’t formally recall the product. That’s now officially happened, with the recall registered with the Consumer Product Safety Commission.

Despite the legal recall, consumers don’t have to send the alarms back. Instead they can check to make sure a software update issued by Nest to disable the wave feature is applied. Once the update is in place, the button for wave in the digital control systems (accessed on a computer or smartphone app) will be set to off and grayed out so that it can’t be switched back on.

While Nest is offering a complete refund to any owners of the alarm, the only formal change that has come with the CPSC recall is that it now becomes illegal to sell the product (including reselling used items) until the recall is formally closed.

The alarm is the second product from Nest, which made its name with a home thermostat system that could be remotely programmed and automatically adjusts based on your actual usage patterns. The Nest alarm includes features such as an early warning voice message (meaning you don’t get an instant piercing sound for false alarms), automatic lighting that comes on if there’s an alert at night, a visual check when you switch your lights off at night to confirm the battery still has power, and a CO2 detector that automatically switches off your furnace if you have the Nest thermostat as well.

Earlier this year Google bought out Nest for $3.2 billion, though opted to keep it running as a largely separate entity.