While Replicant is a fully free system, other components run aside the system, such as bootloaders, firmwares and the modem operating system (if applicable). These components are usually proprietary software. Some devices can also run free software bootloaders: see the documentation specific to each device for more details.
For more information about these issues, read our freedom and privacy/security issues page.

While fully free software modem firmwares like OsmocomBB do exist, the only supported smartphones (The Openmoko GTA01 and GTA02) are probably not powerful enough to run recent versions of Android decently as they have only 128M of RAM.

Replicant only runs on the listed supported devices . Other devices have to be explicitly ported to Replicant: specific drivers and configurations have to be written so that Replicant can handle the device properly. It is not a good idea to try installing an image for a device that has a similar name: it will fail and may damage the device.
You are welcome to get in touch with us and start evaluating your device as a next target for Replicant!

While Replicant is a fully free system, some proprietary components that are not part of the system, such as bootloaders, may still be executed (the situation depends on each device). These proprietary pieces have access to the data stored on the device. Hence, they represent a risk for security.
On telephony-enabled devices, if the modem is poorly isolated from the rest of the device, it may also be able to compromise the data stored on the device and apply software changes.
Despite being fully free, Replicant may also be exposed to security issues that were not disclosed and/or fixed yet, like any operating system. Just as well, installing third party applications may bring security issues, especially if they come from untrusted sources. Of course, installing any proprietary application creates a risk for security.

Communications made using the public mobile telephony network should be considered unsafe by nature, as the mobile telephony operator is always able to record and track these communications and is often legally allowed to do so. In addition, it was shown that in some cases, these can be intercepted as a result of the weak encryption in use. Safe communications can be achieved using encryption over the Internet (e.g. through mobile data networks).
However on telephony-enabled devices, if the modem is poorly isolated from the rest of the device, it may be able to access the microphone of the device or access the communications data unencrypted, making any kind of communication unsafe.

Most of the time, hardware features are driven by proprietary software in LineageOS. While Replicant is fully free, these proprietary parts are either replaced or avoided in Replicant. Such parts being avoided instead of replaced is the result of missing free software support for that hardware. It happens because developers failed to write free software support for that hardware, as a result of incomplete or missing documentation from the manufacturer, lack of time to perform reverse engineering or generally speaking, lack of proper resources.
Keep in mind that writing free software replacements is a technically complex task that does not always succeed, especially when the manufacturer doesn't communicate how to use the hardware.

Replicant uses LineageOS's source code as a base. It is rebranded to provide the Replicant look and feel (wallpapers, logos) and parts of the code are reworked to remove anti-features that can spy on the user. Most importantly, Replicant does not include any of LineageOS's proprietary components (programs, libraries, firmwares) and instead provides free software replacements for some of these. The rest of the system is also adapted so that the free software replacements can run correctly.

LineageOS supports more devices than OmniROM, which makes porting a new device to Replicant easier. On top of that, most if not all devices that are currently supported by Replicant are not in OmniROM. OmniROM's general position may be more friendly towards free software, but it still ships with proprietary software.

Replicant is a free software project and thus does not encourage nor enforce the use of proprietary software. Shipping proprietary software is a way of taking the decision for the user to use proprietary software, which is not an ethical nor respectful thing to do.

Replicant is a free software project and thus does not encourage nor enforce the use of proprietary software. Providing instructions to install such components is a way of encouraging the use of proprietary software, which is not an ethical thing to do.

One of the goals initial of projects like GNU or ReactOS was to replace nonfree operating systems, like Unix and Microsoft Windows. To do that they could not simply reuse the nonfree operating system source code as it wasn't free software, so they had to write their own code and reuse other available free software components.

With Android the situation was much easier because even if many drivers were not free software, most of the operating system source code was available.

So with way less effort, we could have an exact Replica of Android with the same graphical interface and so on. We just had to replace these nonfree drivers.

When trying to find a project name, "Replicant" looked neat as not only we were Replicating Android, but the name was also loosely related to Android as in Blade Runner, Replicants are also Androids.