How do I install a chain lock on a steel door?
As @DA01 mentioned, a good 12 volt drill should manage this just fine if you are using a drill bit designed for metal. I have had metal doors on my last three houses, and all were easy to drill.

If you are using a battery powered drill, it may have lower torque than a wired drill, but that wouldn't be a problem here - as long as the battery lasts until you are in:-)