How can I find if someone is using a gsm jammer in my home?

If you have other symptoms that lead you to suspect then I would suggest a suitable frequency scanner with direction finding to check that there are transmissions in the cellular frequency bands, when and where they are coming from, and if this is a different direction from your local cell tower.
So, what are the symptoms that suggest jamming is taking place? Indoor coverage can be less reliable because signals can be blocked/interfered with by stone walls, wire mesh forming a Faraday cage (including ‘fake’ leaded windows) and insulation involving metal such as tin foil. I would also check with a friend who has a cellphone on a different operator (and so frequencies) to see if they get the same effect, as well as trying to force the phone to use only 2G say, or 3G, to try and localise the problem.