Alarm calls in response to potential danger are widespread among mammals. We conduct a detailed analysis of alarm call acoustic structure in wild-living giraffe (Giraffa camelopardalis), sambar deer (Rusa unicolor) and Indian muntjac (Muntiacus vaginalis), and describe their vocal behaviour while mobbing people. Giraffe alarm calls represented broadband hisses of duration 0.24-1.04 s and the peak frequency at 0.69 Hz. Sambar alarm calls represented tonal barks with arc-shaped structure, the maximum fundamental frequency 0.98 kHz and the depth of frequency modulation 0.34 kHz. Muntjac alarm calls had much weaker frequency modulation, a maximum fundamental frequency 0.66 kHz and the depth of frequency modulation 0.10 kHz. Comparative data (our own and literature) suggest that ruminants have a few types of alarm calls. In giraffes, waterbucks, impala, Siberian musk deer, goitred gazelles and Western turs, the hiss, hiss-whistle and snort alarm calls are produced through the nose with an aerodynamic whistle mechanism. In sambar deer, Indian muntjacs, white-tailed gnu, greater kudus, red deer and sika deer, the bark alarm calls are produced through the open mouth and display a clear fundamental frequency. In the springbok and klipspringer, the fundamental frequencies along the aerodynamic whistle are presented. No evident relation between nasal or oral emission of the calls and animal taxonomy or habitat can be found. This suggests Ruminantia as a good model taxon for investigating the role of acoustic diversity in vigilance and alarm communication, in addition to the traditional model groups, birds, primates and ground-dwelling sciurids. Supported by RSF grant 14-14-00237 and RFBR grant 15-04-06241.