Let's look at what is available and what you need for your keychain.
Available:
1) Security Keychain Remote (KR10A-COM)
Arm and disarm your X10 security systems, Turns on and off everything on 1 house code.
2 )SlimFIRE Pocket Remote (KR19A) Turns on and off 2 lights/appliances on same house code.
3) Credit Card Controller (KR22A) Turns on and off 4 lights/appliances on same house code.
Need:
A) A keychain sized remote that can arm and disarm security systems.
B) Can control at least 2 different house codes.
C) NO reason X10 couldn't make one, possibly like this.