Do you mean those cheap 433mhz / 315mhz OOK RF transmitter/receivers?
Those use automatic gain control, and adjust their sensitivity to give ~50% duty cycle output, allowing them to work under a wide variety of ranges and conditions without adjustment. As a consequence of this, you get random gibberish out when there's no signal, as it amplifies noise until it gives 50% duty cycle output. You also get random gibberish if you leave the transmitter on, as it cranks the sensitivity down until it gives 50% duty cycle output. The only way to transmit data is to send a pattern with ~50% duty cycle, and send it several times to ensure receipt (often you may also see a "training burst" with 50% duty cycle at the start of a set of data So you need something with some smarts on the receiving end.
You can get something like this, though, and "push" the buttons on the transmitter with the arduino (IIRC the buttons ground a pin of the IC when pushed) - these have an encoder and decoder chip on them. (no specific endorsement of this vendor; they also make ones with relays built in and stuff - search 433mhz remote control 4 channel ) IC2262/2272 4 channel wireless remote control kits 4 key wireless remote 433MHZ | eBay