and cheap 433.92 MHz OOK transmitter.
https://teknokoodiradio.vuodatus.net/lue/2019/05/decoding-silvercrest-wireless-doorbell-with-arduino

#include <RCSwitch.h>

RCSwitch rcs = RCSwitch();

#define DATA_PIN      4
#define PULSE_LEN     500
#define PROTOCOL      1
#define TX_REPEAT     48
#define TX_STR        "111110111001001101001000"
                                
void setup() {
  pinMode(DATA_PIN, OUTPUT);
  rcs.setProtocol(PROTOCOL);
  rcs.setPulseLength(PULSE_LEN);
  rcs.enableTransmit(DATA_PIN);
  rcs.setRepeatTransmit(TX_REPEAT);
  rcs.send(TX_STR);  
}

void loop() {
}