Not turning transistor on at 2.7v ??

I am using a transistor 2n3904. I have the middle pin connected to pin4. I am using an Arduino nano pro 8mhz using a coin cell battery CR2032. I am currently at 2.7v from the multimeter and I cannot fire the transistor. Am I missing something?

You're missing the resistor in series with the base to limit the base current so the transistor and/or arduino aren't damaged.

You're also probably missing something else, but you haven't told us what you have the other pins connected to, so we couldn't say what.

I am connecting 1 transistor to sensors, Ultrasonic and Temp sensor, and the other transistor is connecting to the sleep pin on xBee radio

That's a lot of things, please post a drawing/diagram of all the connections. One or more of them are wrong, or there's something else wrong with your design, but if you won't show us your design, how could we give you any help?

Did it work when your 3v3 was really 3v3 ?
Can you draw a schematic of how the transistor(s) are wired?

brolly759:
I am using a transistor 2n3904. I have the middle pin connected to pin4. I am using an Arduino nano pro 8mhz using a coin cell battery CR2032. I am currently at 2.7v from the multimeter and I cannot fire the transistor. Am I missing something?

Yes, a CR2032 cannot provide enough current for your circuit. Its rated for 2mA or less if I remember
correctly. Try to pull much more than this and it won't manage.