(Expanding on Pieter’s comment above, and explaining the logic behind it…)
if() evaluates the conditions in the parentheses, and that evaluation results in either TRUE or FALSE for the sum total (which can change, depending on how the various conditions are combined).
In plain English, if( !is_singular('device') || !is_front_page() ) means, “If it’s either true that this is not a single Device post, or true that this is not the front page, then…”
Since a URL on a WordPress site isn’t going to both be the front page and a single post (unless you’ve gone out of your way to configure it as such, I suppose), you probably want to use && instead: if( !is_singular('device') && !is_front_page() ){}
In plain English, the latter if statement means, “If it’s both true that this is not a single Device post, and true that this is not the front page, then…”