Secure boot affects almost all current smartphones. These devices, in general, ensure that only properly signed firmware is present before it boots and provides access to the files on the device. This prevents some bootloaders from being successful at flashing the device for additional access.

Secure Startup makes the device extremely secure and is offered on devices that enforce Full disk encryption. Most devices do not have it set as the default, although some rare devices may have it as a default option if you select "okay" through the out-of-the-box new phone setup experience. If set, Secure Startup can be a showstopper because we need that passcode in order to access the data in a decrypted state. You will know immediately if a device has Secure Startup because, upon powering, it will require the passcode (not a biometric) to even boot!