Safety Technology International, Inc. STI-34601 Additional Wireless Doorbell Button, 8-Channel Receiver or 4-Channel Talking Voice Receiver (Speaks 53 Words, English or Spanish) Required, Sold Separately Additional doorbell button for STI wireless chimes Series, requires receiver sold separately Easy to install no expensive through-the-wall drilling Water/weather resistant for outdoor use Operates up to 500' (line of sight) Limited one year warranty