Augmented reality startup Magic Leap has started to send a limited number of its headsets to developers, but is asking them for extreme security measures to prevent leaks: Devices need to be stored in a locked safe when not in use, Bloomberg reported Friday.

Magic Leap has been working on its augmented reality headset, which is capable of overlaying digital objects over a view of the real world, in secrecy for years. The company gave the public a first look at its hardware in December, when it announced that it would make a developer version of the device available in 2018.

It also recently opened up its developer platform to approved partners, allowing third-party developers to start building apps for the headset.

However, only a few select developers have actually gotten their hands on Magic Leap’s devices, and those who wanted to be part of this first wave had to commit to strict security rules. These include storing them in a locked safe. At least one company decided that these rules weren’t worth the hassle, according to Bloomberg

Magic Leap has only shown its hardware to industry insiders and reporters willing to sing a strict non-disclosure agreement, effectively barring them from sharing any unannounced details about the device. The company has been able to raise more than $2.3 billion from investors including Warner Bros., Legendary Entertainment, Google and Alibaba.