I put omegas in my text as needed using a command:
\newcommand{\ohm}{$\Omega$ }
Then I needed other symbols so I included package gensymb. But when I do, \ohm is already defined. So I tried using the one defined in the library. It does not add a space afterward, not sure why. My \kohm and \Mohm work fine. I'm not sure whether I should be overriding the \ohm command. What is the best approach to solve this problem?
MWE:
\documentclass[12pt]{book}
\usepackage{gensymb}
\newcommand{\fahren}{\degree F}
%\newcommand{\cels}{\degree C}
%\newcommand{\ohm}{$\Omega$ }
\newcommand{\kohm}{k$\Omega$ }
\newcommand{\Mohm}{M$\Omega$ }
\begin{document}
test \ohm
test \kohm
test \Mohm
I measure temperature in \fahren
\end{document}
I do not want to have to add braces or a backslash after the command: \ohm{} or \ohm\
The \kohm command works as I want it to, inserting a space afterward because it is an equation. I suppose I can define a \ohm command that is exactly the same as \kohm but then I would have to replace every one of the \ohm commands in multiple documents.

siunitx, which creates a complete interface for units. – Manuel Aug 03 '16 at 22:57