433Mhz receiver only get values of 0, 1, 2
Those cheap 433 MHz RF modules require a (good) library to work. The VirtualWire/RadioHead library is the best.

The VirtualWire library it outdated, but still used.

The RadioHead library has a few bugs fixed, but uses more memory.
Use it in RH_ASK mode, see the included 'ask' examples.

[Update: better quality]
Most cheap 433 MHz ASK transmitters work with 3.5 to 12V. They have the longest range at 12V. About 20 meters is no problem with 5V, but if longer range is needed then transmitters that are only made for 5V are better.
The cheap 433 MHz receivers use a coil to tune the frequency. They are very sensitive and they do work well. However, when such a module is placed near metal or close to the Arduino, the frequency might change. Modules that use a crystal for the frequency are better. Sometimes a sensitivity is mentioned (for example -112dBm) but I don't know how reliable that is. When an antenna of 16 cm does not work well, try an antenna of more than a meter.

The transceivers are better for wireless data transfer, but that depends on the use.
Sparkfun has Wireless Buying Guide.
RadioHead has a list of supported transceivers.

The nRF24L01+ are very cheap. I read that every one of them on Ebay or Aliexpress is counterfeit, but the counterfeit chips do work. They work at 3.3V, and are 5V tolerant.

The CC1101, CC2500 and so on are good, but not often used with an Arduino. The same for Si4432, Si4436 and so on. If you know a good library, they are very good transceiver chips.

Adafruit is using the RFM69 a lot. For example the Feather Packet Radio board.

Last but not least: don't forget Wifi and Bluetooth.