Small hobby project

I have never designed any radio stuff

I want to solder together a nice thingy that will flash when my GSM telephone rings.  Yes i know there are plenty designs already out there but i want to use my solering iron...

I thought of connecting a LED and NPN transistor in series on a coin cell 3V lithium, and a 900MHz resonating cirquit to base-emitter.

But i have no experience how to make the resonating antenna, I thought of a small loop of wire, with a very small ceramic cap inserted in the loop.  One side of the cap also connected to the transistor emitter, the other to the base.  When amplitude reach 0.7 V the transistor conducts.  (only part of the cycle but that does not matter)

Better ideas?

Use a HF diode in series with base, to limit the base capacitance influencing the resonator?

Using a slow transistor i hope to be safe from it self oscillating; i do not want to make a transmitter...

How do i design the resonator? 
Are there some rules of thumb, then trim by selecting cap or bend the loop until i get it to detect at the longest distance from the phone?

It would be very nice if it could also detect 1800MHz, but i think that would need separate loop and transistor for each frequency?  Or can i make it dual resonating using only one loop antenna, then add an additional inductor (chip type) and cap to resonate at the second frequency?

/Morgan HF beginner

Morgans Reglerteknik,   HŠllekŒs,   277 35 KIVIK,      SWEDEN
tel +46(0)414-446620, fax +46(0)8-59817928, morgans.rt@telia.com